Sorry this will probably be long - hoping some brides can help that maybe aren't as naturally aggressive in these situations as I can be

So I asked about this girl awhile back - my fi's good friend he wanted in the wedding - asking which side she should stand on - we asked her she said shed feel awkward on the guys side so she's on mine - fine - at that point we were getting along - now not so much and i don't know how to handle it because my natural reaction when a friend acts really badly is to talk to them about it and if it happens again take it as a red flag - separate myself - and move on with life - for reasons I'll explain this is not possible.
Ok so this girl dated the guy who was supposed to be our best man for 8 years - naturally my FI and her became friends because he lived with the BM for 6 of the 8. Anyways - not trying to gather sympathy here but it's relevant - he passed away last October - at 27 - not expected - my FI wanted her in our wedding - I think it has a lot to do with in someway that keeps his friend there if that makes sense? So after that happened I kinda became a rock for this girl in terms of the BM - I was there the whole week in the hospital etc and basically took care of her and my FI and so we became close after that week - she emailed me daily - numerous times a day (lives in MN) and I was always always there for her. I was happy to do it - she was important to my FI and I thought we were becoming friends on top of that. About a month and a half ago now she completely started ignoring me - not responding to emails, calls, texts. It took my FI till this weekend to bring it up to her cause he kept saying she must be busy and he hates confrontation. This is what she said to him and I'll try not to make it confusing - my last email when she stopped responding was about my friends wedding coming up on Boston next month - the BM was from Boston so I said my FI had called his parents and we were going to stay at their house Friday and at the hotel of the wedding Saturday. This upset her because she didn't think she should find information out about my FI and the BMs family from me and she felt if she kept talking to me everyday eventually that's how it would be so she decided to stop responding - completely - to everything! Doesn't even respond to a group BM email I sent asking their opinion about dresses. I
Kinda not getting her logic but that's besides the point. So now honestly I'm pissed - I spent so much time and energy consoling her and talking to her and being there for her and everything and she can just drop me like that - obviously the friendship I thought we were forming wasn't there and I kinda don't want her as a bridesmaid anymore - I can't kick her out cause she matters to my FI and he wants me to try and email her again but I everytimr I start I get mad and it comes out aggressive - I'd rather say screw you too - but I can't - so what would you ladies do if you had a bridesmaid who refused to acknowledge you exist but you couldn't kick her out? I can't really talk to my FI about it cause he gets sad about his friend. Thanks and sorry so long!