If you feel comfortable talking with her about it, then just ask her whats wrong. If you don't, then maybe lay off her for a while and see what happens, see if she calls you and such, if she does then obviously she still must have some interest in you.

You said that you hooked up one night but things got too touchy feely and she said things were going too far, maybe she feels that you went too far and she just wants to slow things down? Since she was in a serious relationship before, even though she may be over the last guy, it may still be difficult for her to do things with you until she's comfortable.