Life advice for a 22 year old not getting along with her future mother in law?

I apologize in advance for the long post as I have no idea how to really cut this down.

A little about myself: My fiance and I met back when we were in high school and have been dating for three years, nearly two and a half of it long distance, and we have been engaged since last August. Shortly after the engagement I finally moved in with him, to his insistence, this past January finally ready to take the plunge of living together and due to lack of available work where I was previously living. We're currently living in his dad's old house with his older brother due to a combined factor of lack of income to live anywhere else (for my fiance and I) as well as an agreement between him and his parents that they would help pay for all his college so long as he agreed to live here. Just to note, his parents are divorced and have been for some time now. As well as his dad lives now on the other side of the country and mother lives a half hour away from us, which means, unfortunately, frequent unplanned visits from her during mine and my fiance's sleeping schedule as he works second shift.

Up until after a couple months of moving in with my fiance, she and I got along very well. Almost instantly I was accepted into the family when he and I started dating. Over time though I have observed that she and I are opposite personalities. I'm more of a laid back type while on the flip side she's more high strung to the point where she can become a total bitch to people. Quoted by those who know her as well as seeing it happen in person all to frequently. I'll be up front and honest when I say I was shocked the first time she lashed out at me. One day in March she managed came to the house while I was alone, cleaning none the less, with no warning and after some polite conversation seemed to turn a 180 and full on verbally attack me over her oldest son calling her all the time because I wasn't cleaning to their standards. Even though her oldest is 29, at that point didn't communicate at all to me or my fiance his frustration, and I managed to keep the house fairly clean despite the claims against me. I.E. - the worst I have ever let the cleaning go was a small amount of dishes that would sit in the sink for no more than a day and some small piles of dog hair that would gather up because, hey, we have a big dog that sheds constantly, thus unless I were to follow him around all day with the vacuum, I never will 100% keep up with keeping the floors completely dog hair free. I should also mention that out of the three people in the house, I am the ONLY person who cleans 99% of the time with the occasional help from my fiance on his days off. Since then she's gone on to berate me due to my lack of finding work and how it's “hurting her son” as well as going so far as to call me “lazy” and a “child”, despite that fact that I have put in dozens of applications and shown her that I am trying. She's even gone as far as to invade our privacy by going into our room while we're at home as well as while we're away to look for god only knows what. While I do understand where she's coming from on the job part, I feel she's over stepping the line quite a bit by coming by unannounced, berating me for things I have no control over, and entering into our privet space without our consent.

Things between her and I have gotten pretty bad. Several times over the past six months she has threatened to kick me out, though she does not have her name on the house. A couple months ago she got so angry with me that she threatened to put her hands on me, by saying she'll physically pick me up and throw me out of this house be damned how I look, all because she showed up unannounced and we were still in bed sleeping at 10 in the morning, even though this is during mine and my fiance's normal sleep schedule. Then a week ago, upon finding out from a friend of ours later that day, after she couldn't get a hold of either of us and noticing we weren't home, proceeded to go to one of our known vape shops we frequent and loudly caused a commotion to all those in the shop about me! I still have no idea what it was about and I'm honestly still confused as to what she thought this would accomplish seeing as I was not around to hear what it was about.

To be honest, I've gotten to a point I've become so afraid of her that I avoid her at all costs. If she calls, I ignore it. If she comes by, I try not to be at the house unless she unexpectedly drops in without warning. Even then, I tend to avoid her as much as possible. She is kind to my face when others are around, but if it's just by unfortunate accident that she and I are alone, she verbally attacks me.

My fiance doesn't want to stand up to her due to fear of her pulling her funds to help him with school as well as he doesn't like confrontation despite that fact he himself is not overly fond of her. While I can't blame him on his thinking, I have made him aware about what is happening as well as my feelings about the situation.

I honestly feel at a loss here as to what to do. I love my fiance dearly, but this constant cycle of issues is starting to push me away to the point where I just want to get away from his family.