There is no way for us to begin to guess her motivations based on your posts. Maybe she misses you, maybe she just wants the thrill of knowing you still care, maybe she really does think you should be over it by now.
Her reasons don't really matter. Its how you feel that you need to deal with. Sounds to me like you are still confused and hurting, so I would recommend you NOT go out with her until you get sorted. Preferably once you get a new GF and have completely lost romantic interest in your ex. You don't need to be cold to her, just be busy.
Since you are already going out tho, keep your expectations low and pay attention to how you really feel when you meet. If you are still hung up on her, then you should do what I already mentioned.
Breakups and 'friends' after is so icky. Good luck.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh