What would you do in this situation (family feud/wedding)?

Sorry, this is a long one. I am the middle sister of three and my older sis and I are supposed to be bridesmaids for my little sister's wedding next week. My older sis is ten years older than me and my other sis is three years younger than me. My older sis has very deep-rooted issues with me personally as when I was in 14, her husband at the time (who she is still on good terms with) tried to make me do something inappropriate and this contributed to the breakdown of her marriage. This was nearly 20 years ago now but the issues still remain. There have been countless times, particularly this year, that we have been having a great time together but then she has too much to drink, turns on me and attacks me for no reason, resulting in huge, soul-destroying fights. Earlier this year, a guy was following me around like a puppy on a night out and she let rip at me for being too weak to tell him where to go before telling my little sis that I had once had a clinch with her fiance (later proved to be completely untrue). I was forced into a reconciliation for the sake of little sis's wedding and since then, we have got on well. However, last weekend, it was my little sis's hen weekend. We had a brilliant time but on the last night, my older sis started ignoring me on the way back to where we were staying, packed her bags at 3am and went home, leaving us to clear up the whole apartment ourselves before checking out the next day. I am still completely stunned and very angry that she did this and just abandoned us so unexpectedly, but my dilemma is that my mum and little sis are forcing me to make things up with her and be amicable for the sake of the wedding. They told me that my older sis was desperately sorry, so I started to hear her out on the phone last night, but she just said "Sorry for what happened over the weekend but I do still have issues with you. I think you're a dishonest person and you are always slagging other people off." Mum and little sis completely disagree with these allegations against me and have told my older sis she is wrong, but they have put the ball completely in my court now. I have to either be nice to this person (who has ripped my personality apart, clearly hates my guts deep down and is still maintaining her issues with me after six months of getting on really well) or I ruin my little sister's wedding. What would you do?