shakti

Funny. Once I went on 2 dates with a girl, and then she said the same to me.
...And then I talked to her about a month later, after we had kissed once and never even cuddled. And she was like, "Oh yeah, actually I think I am straight."

So, you should call her on it. Ask her why she wants to take it slow if she hasn't explained it, ask her what obstacles she might need help overcoming to date you. If she isn't going through some major emotional issues or an abuse victim, then she could just be a bi-curious like the one I dated. She also may be ok, but thinks that dating you is something she can put on the back burner indefinitely.
I don't waste my time with girls like that anymore.