At first I thought it was kind of rude of you to want to cancel at such a short notice. Though, now I can totally see why you're not feeling sure about attending. I see two options:
1) Call her up and explain that you can't go because still feel hurt. You can explain that you are concerned that the bad feelings will only add a negative vibe to the happy occassion. Say that you would feel bad if that vibe somehow carried over on to other guests or even her. Figure that, if she's going to continue to refuse to acknowledge your feelings, then she's probably not a friend for you.
Furthermore, you bought items with the intention of participating in her wedding. It would be one thing if you were keeping the dress. However, she is giving your dress to your replacement and therefore must pay you the $100 deposit back. You didn't quit, she fired you. She can't keep your money. If she does, I hope you all go on People's Court 'cause I'd like to hear what the judge has to say about that.
2) Suck it up and go. Be a gracious lady. Give them a modest gift with your warm wishes for a happy marriage. Hope that you are seated far away from her - fade into the background if necessary. Enjoy the "free" dinner. Duck out from the festivities early if you can do so without being obvious. Then, a few weeks later, inquire about the $100 reimbursement. See if you can have a talk about your feelings. If she still thinks you were childish...just drop it. When you get the check, write a thank you note acknowledging the payment and then promptly drop her from your list of friends.
I'm favoring option #2 as it's probably the right thing to do. It won't put out anyone's catering orders, no one can be mad at you for acting like a true lady and graciously giving a gift even though you were wronged, she can't use your absence as ammunition, and she just *might* get over herself after the wedding and sheepishly realize what a bridezilla she was.
Good luck!
.....Kelly
