How would you feel if you were me?

Wow, that would make me really uncomfortable, too! I would definitely talk to her about it and say that the most disturbing part is that she wants to hang out with this ex knowing that the ex wants her back! I mean, you can't forbid her to hang out with her ex, and it is probably completely harmless, but. . .yeah, that would definitely bother me, too. I'd say just try to keep the communication lines open. Good luck!