In your place, I would just limit contact with her as much as you can, and ignore her spew when you have to talk to her. She is just trying to bait you into some sort of argument. You will gain nothing by engaging her.
She sounds like my XW--extremely insecure. She may be making up stories about students asking her out, or she may be leading them on to get the attention. Either way it's about getting some sort of male validation. If you engage her on this subject, you're just giving her what she wants. Also she'll turn it around on you, claiming that you're obsessed and can't "let her go." It makes her feel important.
Keep notes of all these kinds of observations. At some point her behavior may reach the threshold of being a danger to your daughter. It may never happen, but if it does, you'll want to be prepared.
You're doing fine Rob. It will get less unpleasant with time. Soon you'll be able to just shake your head and think "what a loon."
