Fishkiller,
Play hard to get, don't give her any attention whatsoever, and don't answer your phone.
Woman are crazy in the head, that works every time. The more you baby them, the more they walk all over you. Act like you could care less if she spent time with you, give it 2 weeks, she'll be asking you to go out and do all kinds of things with her.
Agreed, girls nite out is a blessing most of the time. If she didn't want you to go out with her on her birthday, that would raise a red flag for me though.