A child does not have to be biologically yours for you to love them like your own. Sounds to me like your raised her and she is your daughter. I have two kids, not mine biologically, and I never call them step kids unless someone asks (we have different last names). I would go and make it a very special day for YOUR daughter and make that POS fell like crap for not being the father that he should have been. He will always be her "dad" but your her Father. Who cares if he and her mother are going to be unconfortable, good they should be. Just ignor it and do everything to make it the best day for your daughter.

I have been in this type of situation several times and I can tell you this. In the years to come, you will either will be saying "I wish I would have gone or I am glad I did". Be glad you did.