Jim, if I were you I would be careful to talk this out with the woman so you don't get blindsided.
If you and she made an agreement not to have sex, and then she continues to behave provocatively towards you, it's possible that her trust issues are running her unconsciously -- she might be acting out a little scenario to prove something to herself (about her desirability or the trustworthiness of men, etc.) and you can't really win if you're operating in the dark (so to speak!
).
I think it would be a good idea for you to bring the discrepancy out into the light -- to help yourself and her understand what's going on between the two of you emotionally. If you simply let the relationship slide into a a sexual one without being clear with one another, it's likely that some "reacting" will happen, leaving you wondering what the hell is going on.
You don't want to later hear, "See? I knew couldn't trust men! Even you, Jim, whom I thought I could trust!" It's kind of a blind set up.