CAN YOU BELIEVE THIS???--kind of long but i need help!

Ok so a girl i used to be somewhat friends with, is not speaking to me. She knew i got engaged in october of 2006 and set my date for June 28, 2008. She got engaged (mind you to the third person in 2.5 years), about 5 months ago. She set her date for June 27, 2008 which didn't bother me because i wasn't inviting her to my wedding and i didn't expect to be invited to hers. So i talked to her for the first time in months last night and she asks me to be a BRIDESMAID!!. I almost fell on the floor So i had to decline because at that time i don't feel like i can give it my all as her bridesmaid, plus i dont feel close enough to her to be her bridesmaid. Then she says 'so i guess you're not even going to come to my wedding now?!' I felt bad but i cant see doing all of this planning and then being tired for my own day because i went to her wedding the night before. If she was a good friend i'd be there in a heartbeat but to be honest there is a reason i'm not really friends with her anymore (long story short, i broke up with a guy after dating him for 3 months, he started dating her and she knew it was just to spite me). There are other reasons too! She caused a lot of drama in the past. Am i wrong??