I felt somewhat the same as you except it was for my sisters wedding. I really didn't want to go but of course I was one of the bridesmaids so had to go.
I really didn't agree with the wedding but went because she is my sister and it was her special day and I know she wanted all of us there (even our mom didn't want to go) but we just grinned and stuck through the whole ceremony and everything. Because we were not doing it for us but for her.
I would definatly try my best to stay through most of the wedding and party afterwards. How do you think your daughter will feel if you left? You don't want to cause any tension between the two of you now do you? I would hope not. You may also regret it later on if you don't stay either.
Do not go to the stepmother's level and be strong. You will make it you will see. And I am sure you will a ton of other people there who will keep you occupied and you will have a great time.
Good Luck!
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