I don't know what you plan on learning from confronting her, but if she's giving you some bullshit excuses she isn't going to give you any honest answers. It's tough being the rebound, and I'm sure you learned from this experience that maybe some people should be on their own for a little while before you try to get serious. Sorry you gotta find another prom date on such short notice.
If you don't want to be friends with her, don't buy into this. You sound like you are taking it well but if it hurts you, don't let her come to you whenever she feels like it.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.