I don't like my soon to be Sister-in-Law and it's causing issues

I don't like my partners sister. Maybe it's the age difference between us, she's 17, I'm 24 and partner is 23. She never speaks to me or replies to any texts or facebook messages I send, even if they're praising or congratulating her. She never even likes my comments when I comment on her statuses even if she likes every single other comment.

Or maybe it's because I just don't like her. I've tried, honestly I have. But I just can't like her.

I do wonder if I'm jealous, on behalf of my partner who was made to pay board from age 15 right up until he moved out when I was 6 and a half months pregnant, and even when he moved out he was expected to go back and "help his family" by walking their two large dogs which would take anything up to 3 hours a night as the dogs can't be walked together, and then he'd be asked "Can you just wash the dishes" or "Can you whip the hoover round" because you know his dads back was hurting and his mum had been at work all day. And he'd do it, because thats the type of guy he is, all the time his sister would be sitting there not paying a penny or lifting a finger. And don't even get me started on her refusal to look after or walk the dogs despite begging her parents to get them. I put a stop to my partner going over to walk the dogs when my daughter was born, but he still gets asked at least once a week to help, at least now he can usually say he's working or something.

Maybe I don't dislike her but in fact dislike her dad, my soon to be Father-in-Law. Who's idiolised her and given her what she wants. Who made it clear to my partner he never wanted a son, who shouted at him when he lost his job despite it being the fact the company was closing down (so no fault of my partners), and who called him lazy, ignorant and stupid when he found out I was pregnant. Who refused to help his son learn to drive but paid for his daughters lesson and then bought her a brand new 16 plate car when she passed her test - oh and a private number plate too - which must have cost upwards of £10k. Who tells my partner he's lucky to get Christmas and Birthday presents at all because he's useless and doesn't deserve them (despite working 50-60 hours per week sometimes til 11pm at night often doing 9-10 hour shifts and then being woken up, alongside me, by our daughter anything up to 6 times a night), then spends hundreds and hundreds of pounds on his daughter buying new Iphones and Ipads because "she works hard and will do well for herself".

Maybe I hate her because she threw a strop because I refuse to let my 9 month old be driven around in her car, and her parents told me I was being ridiculous and making problems where there are none despite her boasting about driving around after being in the pub with her friends or her boasts about driving above the speed limit. Maybe I hate her because her parents told me I'm no longer welcome in their house until I apologise to their spoilt princess and allow her to take the most amazing, beautiful and precious person in my world for a drive. I'm terrified she'll have a crash and my daughter will be killed in it. I wouldn't get in the car with her so why on earth would I let a defenceless baby who can't tell her to slow down or refuse to get in the car if she's drunk?

And yet I feel guilty, because I hate upsetting people, I hate asserting myself and I hate feeling stupid. I'm getting married to my partner in a few weeks time, what happens if this issue is not resolved?

I'm scared my partners not going to like it either and we'll have an argument.

Maybe I don't like her because she could be the reason my partner and I fall out again.