Sometimes, I have conflicting feelings about someone. I desire them, but I'm also not sure I want to go in the direction that sex would take the relationship, or deal with the emotional intensity that sex creates for me, etc.
It's a lot easier to express the desire part when sex really isn't on the table, for other practical reasons.
She might not realize that this sort of teasing isn't the nicest thing to do, given your history, and the fact that that sort of relationship really doesn't seem to practical. If it feels hurtful to you, then tell her.