First I want to thank everyone for the honest advice. it was to say the least very honest. With my own wedding in a week I found myself having better things to worry about. Today our families had a brunch with one another and I ended up finding a perfect moment to talk with FSIL alone. I congratulated her on the engagement and asked if she was very excited.she said yes and said that she was glad cause no one would be trying to take her boyfriend from her now. I genuinely told her that I didnt think it was possible because he loved her too much (which I fill heartedly meant). And I ended the conversation there.
Well she proceeded to point her finger on my face saying that I tried. And I couldnt help it but I laughed. I told her I was not interested nor have I ever been in my FBIL. she then accused me of unnecessarily helping him, like with his car one time. I just explained to her that she was there when he asked me to check the engine on his car because he didn't want to be overcharged at a dealer and I knew what I was doing being a mechanics daughter.
I then apologized for any action that may have seemed threatful to her. But I told her I didnt appreciate the years of glares, scoffs and eye rolling at every comment I made. And I left it at that. I said for everyone's sake we should be civil with just hellos and not anything else because it is not their fault. She then said she really didn't care about her FI's family and she doesn't have to be nice. I was shocked and she proceeded to say it was bad enough she was going to have a busy body MIL who had to know our every feeling. And that she didn't have to say hi to me because she had to deal with our in-laws.
The unfortunate thing about this was my soon to be MIL, FIL and her fiance heard this. I feel a little lost in this because I didn't think she would snap. I regret even congratulating her now because that is what sparked this even though I am happy for her because I know how exciting it is.
Update: FBIL contacted me apologizing saying he would make her apologize. I told him it was not necessary because that would just fuel the situation.I told him to just leave it be and it was done and over with. we both have been acting very immature and stupid about this, and that if she wants to talk to me she can approach me at a more appropriate time. He always said she was angry that I did not make her a bridesmaid in the wedding. I dont feel that I should have because of our strained relation. I had talked it over with my FI and he said he would not be offended since he doesn't care for her either. I don't feel its right for her to force herself into the bridal party and I have given her the opportunity to be included on other parts of the wedding. I am very much over trying to be in healthy relations with her but I will not instigate future conflicts as enough unnecessary damage has been done.