Because she just broke up with her boyfriend, she was probably feeling vulnerable and in need of the company of a friend like you, which led to your date. I'm thinking that afterwards she realized she accidentally led you on, and is probably avoiding what she feels is inevitable: you confessing to her, and her friendship with you forever gone.

It would be nice if you got a hold of her, and asked her what's going on in her life: ask casual things, don't spring anything on her, and from this you can probably figure out how she feels.

I agree with >>48 that it'd be best to let this one go, but just talking to her and getting some closure would help.