I was fired as maid of honor.?

My close friend of over 20 years is getting married for the second time. I was ecstatic when she became engaged, until her fiance became abusive both mentally and one time physically when he was on drugs (5 months ago). She says things are great now and seems to ignore any bad signs. Her family does not know about these episodes. I have found it quite hard since then to have any real enthusiasm over her wedding when I am scared it is a major mistake. She has had an engagement party, which I flew in to attend, then a bridal shower and couples shower. The last two I did not attend because I live 5 hrs away. The wedding is in Hawaii and the attendant dresses she choose were expensive. I have already purchased my ticket and dress. Last night I threw her bachelorette party and everyone had a blast, until her younger sister had a melt down, screaming at me that I didn't deserve to be maid of honor and other expletives before leaving and driving 4 hrs home. After that I told the bride that maybe her sister should be the maid of honor because it seems to mean more to her. I guess that was a mistake. This morning I woke at the hotel and checked my email to find a snide and condescending message from the bride (who was staying in the same room with me) saying that I am no longer maid of honor. She said it was obvious that I am not committed to her happiness, that I have made her feel guilty when she asked me to do things and that I have not lived up to the role of maid of honor. I may still attend the wedding, she said, as a bridesmaid or guest or not attend at all. At this point I am so tired of the drama I just want to not go. This will likely result in the termination of an over 20 yr friendship, if that isn't what happened already. When she asked me to do the maid of honor duty, I thought that meant I was supposed to be supportive, throw the bachelorette party and stand up there with her. I have not responded to her message yet, but I told her I was mad, packed and left without going to the planned lunch. I'm not sure what to do now. Do I go to the wedding? Do I respond to her? Is this friendship even worth saving?