I'd say ask what's wrong, if she just plain does not want to talk about it then walk away.
If you only missed her birthday and she is THAT pissed about it, I'd say the relationship is not going to last long anyway. If this is the case, you can probably patch things up temporarily but I can almost guarantee that you will have issues later.
I went through something similar about 4 years ago and I have not found anyone I want to be with since then so maybe I am not the best person to take advice from... At least it is a more useful post than some of these other a-holes on here.