What would you do if your friend acted like this?

My friend is getting married next saturday and had asked me to be her bridesmaid and I agreed...but, she's been acting funny lately...The whole confusion started over a month ago when she asked me to go to her wedding fundraising and I agreed, but a week later had to cancel because I couldn't make it due to transportation and even told her I would come if she picked me up, but she couldn't. So I sent her a check for $100 to make up for my absense. She never called to say thank you and went on to ignore my call and messages-I called her april 15 and she only returned my call yesterday. You mean to tell me she had time to go on facebook and din't have the decency to call me? She calls me a week before her wedding. I've moved on and decided not to answer her calls because a true friend would have kept me abreast of things especially being I was supposed to be her bridesmaid. She must think I'm stupid!! I bought my dress already, but I'll now return it. What would you do?