That's a tough one, mahhhty. Gogofo brings up some good points in regards to DB etiquette and essentially not letting them have their cake and eat it too (PUN).
However, and this is something that I had to deal with on my son's most recent birthday, you have to consider who you are really affecting with this decision. It might be hard for you to have her at your child's party, but the party really isn't about you. It's about your child. Would it be good for them to have both of their parents at their party? Should you "punish" your child because of your x's actions?
I don't know all the details so only you can know what the right thing to do is. You mentioned that she still hasn't taken you up on co-parenting classes - so i guess I would ask you if you are at all concerned about making a scene at the dinner/party?
Sorry if I am missing the point of your question here or misread the situation. Just thought I'd throw in my 2c.
Keep on keeping on, bud!
Me 23, Her 21 1S 2 M <1yr, T 7 WAW: She moved out 11/15/2014 She started D process 1/29/15