Rude Sister In-Law how to cope????

Hey so I'm in a situation where I'm engaged to the man of my dreams of over 3 years now and we have been friends before for 10 years. My fiance is 33, i am 31 and he has a sister that is 34. My fiance lives at home with his mum, dad and sister still and we are looking to get married at the end of this year and get a house. I have been having some problems with his sister since I met her 2 years ago. His mum and dad love me like I am their daughter. I have been nothing but kind, respectful and humble towards his sister and even brought her gifts and a dress for a friends wedding, I wanted to build a good close relationship with her.

It started 2 years ago, One day we was talking without my fiance present she asked about my hair, she said if my hair was real and if I’m wearing extensions, I said no because unfortunately I had bad extensions put in a long time ago and they ruined my hair i am wearing extensions until my hair grows long and thick again and didn't feel i needed to tell her if i was or not as i didn't want anyone to know but i found it weird how adamant she was being to the point she said let me check then...... i didn't know what to say so i ended up being forced to admit yes i have some in and when i told her, her face lit up and she got all happy saying omg i knewww it!! I could tell!! I was just like erm ok, i felt very uncomfortable by how she kept trying to get me to admit i had extensions. I felt violated and it’s not her business if I have I don’t ask her about her private stuff I respect her privacy when i said No it should have been enough but she kept going on even to the point of asking to look in my hair. I didn’t mention to my fiance at the time I just left it, the next day she txted me and apologised if she came across forceful so I thought it's ok she apologised. But then the next time i saw her in front of my fiance she looked at my hands and said ohh i am so glad you took them fake nails off they look chavy!! I was just shocked with what she said to me and my fiance said to her watch what you are saying! and she went quiet.

I found out from my fiance that when she first met me she was very impressed with how he got me as she said how beautiful, tall and slim I am so I know what she thinks of my looks but has been attacking them since.
My fiance was angry about how she spoke to me about my nails and said to me she doesn’t think before she talks. The week after we was chatting away about stuff in her room and she randomly asked me if I had gotten my lips done I straight up said yer because I am not ashamed of it, and then she said don’t get it done u don’t need it and that she could tell as her best mate is a doctor and does fillers, I just kinda said yeah and I wasn’t offended I just found it strange how she just randomly mentions it as she analyses me or something. I felt like she likes to point out stuff like my extensions my lips and nails. Anyways when me and my fiance left his house I told him that his sister knows about my lips because she asked and I told her, he got really annoyed about the fact she asked and said that he is going to talk to his mum about it as its best because she will kick off and he didn't want to cause an argument.
I later found out that when he got home that he sat down to talk to her about how she talks sometimes to people and she just flipped at him. She got all angry and thought it was because I complained about her to him. He told her that he is referring to the comment that she said last weekend about my nails being chavy, but it got so heated that they nearly ended up in a physical fight with one another and his mum and dad were very upset about the situation. After this argument they had stopped talking to one another for a few months and i felt so bad about this, I didn't want it to have caused an argument between them and fall out as I specifically told him not to tell his sister as she would think I went running to him to cause ****.
I tried to help the situation but when i txted her and said not to worry about her brother and to ignore him she replied back ‘’haha you are obviously bothered because u ran to my brother telling him our girly private talk, I know what ur like now iv got nothing to say to u.’’ I left her to cool down as I thought she sounds very upset still. I was worried about going around the house again because I didn’t know how she would be towards me but she was mostly out when I went around or just ignored me. She even sat away from me at the dinner table when she would sit next to me and her and her brother wouldn't talk.
I tried to make things better as time went on, being there for her and gave her comfort when a distant step brother of theirs passed away, I would make effort and buy random gifts, always say hello and bye even if she had not come to say hello to me when i came around but she would be always a bit distant from me but recently things have gotten better I went out shopping with her and her friend few months after it all and we talked more but still she has thrown more digs at me.

When it was her birthday she had invited me but I said that we can do something ourselves as she was going out late with a group of girls I didn’t know and my fiance is not a fan of her friends. My older sister had her added on her Facebook and she kindly invited my sister to her birthday, my sister accepted and she was excited to met my sister but unfortunately my sisters friend had to cancel as her friend had run into some problems whilst they was out that same day of the birthday. My sister txted her 4 hours before the meet up time and let her know that she could not make it and was very sorry, after that she got kinda annoyed and in a mood. After that she txted me a really bitchy txt saying how my sister must not go to fancy places that she don't know how these places are that if it wasn't for her lovely Doctor friend knowing the manager of the restaurant they would have been charged as they had to reserve a table! Funny thing is my sister has been to all the most posh places in London and knows them all very well and that particular place doesn't charge so she was just saying it to have a dig at me.

After a big things seem to be fine between us after but then when i was out with my younger sister in the car going central London shopping, my fiance's mum rang me but as I was in the middle of giving my sister directions to the location we was going to I said to her that I will call her back and she was fine with it. A little later after we just had parked the car and we got into a shop I got a random message from her saying ‘’I know we look like Barbie dolls effortlessly and all natural so all fake girls gonna hate us lol’’ when I looked at my phone as I saw that message from her, I ignored it and then she messaged me again saying ‘’opps ignore, that was for someone else''. I highly doubt from all her comments that was by accident and not aimed at me! I simply ignored it and said Okay and asked her if she was going out somewhere and she replied that she is going out for New Years, and i then said to her that did u decide to go out then for NY and she replied very rudely ‘’U r txting me promptly but my mum said she called u and u couldn't talk to her!!....My plan to go out new yrs eve was always there.'' I really was shocked by her attitude and how she was telling me off for not calling her mum back when she don’t know that I was busy at the time. I explained to her that I had tried to call her mum back but went it to voicemail and that I was out at the shops etc and she sarcastically said ''shopping its Sunday its prob not as manic'' I kept my cool and ignored it but it really got me so angry, i had tried so hard with her even though my fiance don’t care if we get along or not because he sees it as that it's about me and him not his family but I feel that it's my duty, as his to be wife to make effort and to get along with his family but it seems she don’t know what respect is nor does she have any manners for a 34 yr old.

After all this later I was in the toilet at their house and heard her laughing in her room about hair extension on the phone to her friend saying how natural and long her hair is, I came out of the toilet and she went in a few mins after me and in a loud voice shouted ''OMG THERE IS SO MUCH HAIR HERE''!! I know that when i left the toilet i did not leave my hair in the sink. My fiance heard her say this and her mum got so angry and told her off, she acted all innocent and went off in her room to cry.
I honestly dont understand how can some people behave like this, I don't get why she talks down to me about fake things yet when we was talking about famous women and models she was saying how she found certain ones sooo pretty and they was very fake nose jobs, cheeks, contacts etc and i said yeah but you do know that they have had a lot of plastic surgery and she said well u know you have to have a nice canvas in the beginning it don't matter she is still gorgeous and i said yeah they are, then i said that i love Megan fox and she turned around and said yeah she's so fake though and I'm thinking wtf u just said it don't matter lol.

Later that same day i was in the mirror fixing my hair and she passed me and said did you get thicker extensions i said no and she turned around swishing her hair and said ''ha look my hair is longer than yours'' and i was like erm ok. She has had this weird obsession with flicking her hair around whenever i am around her, my fiance has even noticed and she even does it next to me at the dinner table!!

Honestly she the type of girl who boasts about herself but seems to like to put others down, I said to her one evening as she had got all dressed up to go out that she looked nice and she literally said ''Yeah I know'', no thank you nothing!! I haven't said anything to her because i dont want to give her the satisfaction that she is getting to me because that is clearly what she wants and i dont like confrontations, in the last few months she has not said anything to me YET Thank God but still flicks her hair around at me!!!
I try to kinda keep a distance from her now and I have spoke to his mum about it so she is aware and I think she has had words with her about her behaviour.
After all of this i think she has had a nose job as i was showed photos of her when she was a teenager and her nose was bulbous so i've tried to look closely at her nose when i'm talking to her and i kinda saw a kind of scar under her nose tip so i'm thinking hmmmm what was that you was saying about being natural and laughing at people with fake hair? Honestly I wish there was a way i could ask her if she has had a nose job but I dont know how to go about and say it, i'm not that type of person to be bitchy like her about it, i've asked my fiance but he won't say.

Update 21/3/16 so she went to a Iranian New yrs event with her friend who invited her to go. She has brought a very lovely blingy dress to wear and I was around the house on the evening that she was getting ready to go when she was all ready i complimented her saying that she looks lovely and that she did a good job with her eye makeup and her reply was ''Yeah I know and I know I did'' then few minutes after she looked in the mirror then said to me ''I look so Hot dont I''? I just said yeah as I can't turn around and say No you dont!! I'm not rude like that. The next day she messaged me some of the pictures from that night and I said that the place looked amazing and asked about who sang on the stage. She messaged me saying ''Isn't my friend gorgeous and her dress was amazing... we had one of the best dresses on...''
I had not replied back to that as I went off to sleep. When i woke up i replied and said that i had fallen asleep and that it was so kool she saw some famous singers there and that t would have been lovely to be there maybe next yr all other. Then she bombarded my phone with so any pictures of her and her friend and messaged me saying ''You didn't say anything about the pics. They look great dont they? You like my friends dress?
Then she sent aother message straight after saying this ''Some others our mutual friends are so jealous they dont make any comments and pretend they haven't seen the pics... yet they constantly bombard whatsapp and Facebook with their photos and expect us to comment hahahaha''

Now i have nooo clue what she was getting at as i dont have my pictures anywhere as i dont have a facebook or even pic up on whatsapp but its obvious that she was aiming that comment at me trying to say that i am jealous just because i had not complimented her friend!! I had not see that message first as i was already replying to her saying how lovely they both looked and that her friends dress was very nice and similar to hers.
After that she shut up about it then later as we got messaging each other again randomly during the conversation about famous ppl she again message me this ''Anyways.... when people dont comment about others who look beautiful there's only one interpretation: Jealousy. In general of course... if I see someone who looks beautiful I always say it or complement them.... Do you see what i mean....''
I was soooooooo confused as why she is still going on about it and trying to say that I am jealous?! I just replied nicely that ''Yeah i'm not disagreeing with you, i love complimenting people and making them feel good about themselves. Yeah some people do get jealous but others dont really focus on looks.'' After that she blady stopped with her rude comments! I just dont know how to deal with someone like this who talks to me sooooo rudely for noo reason!!