I am sorry that you are feeling hurt. That really isn’t fun and must be tough.
That said, have you considered that maybe it has to do with her feelings about your fiancé? My mom is someone who always assumes people are jealous of her when they aren’t nice/ responsive, etc., and I have found it usually has nothing to do with jealousy. There’s usually another problem.
Sometimes when a person doesn’t like who their friend/sibling/ family member is engaged to/marrying, it can be VERY awkward. Sometimes keeping one’s mouth shut and maintaining distance IS being supportive in and of itself, because they hate the guy or situation. It’s a matter of employing the old adage, if you can’t say something nice, don’t say anything at all. Maybe because she loves you she wanted to say yes to your bridesmaid request, but now that she has said yes, she is having a hard time so she is avoiding you. (By the way, if this is the case, it’s still not ok that she is avoiding you- I’m not justifying her ignoring you at all, but rather offering a possible reason for it that you may have failed to consider.)
I had a friend marry a guy I couldn’t stand, and the best thing for me to do was say nothing at all. As we had discussed my feelings for him early on when she started dating him, she already knew what I thought, and made it clear that only her opinion mattered. When she got engaged, I had no interest in hearing her gush about her wedding plans to a man who cheated on her and made her cry all the time. When she brought up the wedding, it literally made my skin crawl. It saddened me that her self-esteem was so low that she’s not only put up with the loser, but would marry him while he ran around on her. On top of the infidelity, he didn’t go to college, church, or have a solid career, while she was religious, educated, and successful in her own career. To me, they were a bad match, but no one wanted to hear that. Avoidance of her made the whole thing easier. She told one of our mutual friends that she thought maybe I was jealous because I was less available than I had been, but our mutual friend knew better because she also hated him and I had been very helpful with her wedding. The fact was, I would never want to marry an unfaithful, cheating, atheist without an education or a job. I would have rather died alone than date that guy, but it was easier to just let her think jealousy was the problem
Anyway, the case with your fiancé may not be so extreme, but consider whether or not maybe she may not like him due to something. (Hopefully something smaller like he’s rude and not a cheater). Maybe she is trying to support you by keeping her mouth shut. Maybe she shouldn’t have said yes to being a bridesmaid, but feels too torn about it to know what to do. It’s hard when you want to support a friend, but don’t approve of the choices they make. You try to balance it all out, and that is never easy.