Legal Question in Family Law in California

My legal opinion? Probably not. My advice, seeing what affects divorce has on children? I know that former couples have alot of anger, but it does not benefit your daughter. While you may have a legal right to prevent him from being at the party, I am looking from your daughter's point of view. It is probably more important to her that her daddy be there. Kids have no choice in the breakup of their family. She may have an attachment to the other man, but from your post, I am assuming you are not married. It is a common mistake for parents to have a significant other too involved in the lives of their children before there is a real commitment. It is very unsettling for the child if you two split, and he has nothing else to do with your child (and there is ALWAYS a possibility of that). It would be easier for him/her if (s)he has a steady father figure in his/her life. No judgments here, just speaking from experience from what I have seen kids of divorce go through. I know you love your daughter and want what is best for her. Try to keep peace. Don't bring the boyfriend. Give your ex some time to heal and don't make this an awful birthday experience that she will be talking about to some therapist 15 years from now.

Damned good advice from Ms. Beers.