Man, I hate this hearing this. Let me help you with my own personal perspective based, unfortunately, on past experience.
My ex was w/ her ex for 7 years, on and off, and then was w/ me for a year. When we started dating, he was brought up frequently. There was no surprise considering how long it lasted. He left to Western Michigan on a football scholarship and she declined his sexual invitation before he left because of me, and mind you we'd only been dating a month. That to me was a huge sign, but in the long run, their relationship was always there. It's not that he was brought up every single second, but it was just like a dark cloud in a way. I finally told her after being together for a few months that I didn't want to hear about him or their relationship anymore. And honestly, it stopped there. But in the long run, one reason she said she broke up w/ me was because she went from 7 years w/ him into a year w/ me and felt like we were going to get married and she was never going to have that time for herself.
Now after airing all that, my advice to you is to take it REALLY slow. Don't get attached in any way, shape or form. You've got to let her make all the moves. Seriously. If she acts like you guys are just cool and just wants to hang out, then you'll know that you're a rebound. If she starts talking serious or just starts to show the typical signs that she wants to be with you, then that may be an indication that she's ready to move on. Remember that communication is the key. You've got to get inside her head. This is such a hard thing to give advice about because everyone is different and obviously each relationship is different. Bottom line is just be careful.
