I'd stay away from her. You've already gotten burnt at least once by hooking up with her after the break up and thinking it meant something. It's very likely to keep happening over and over again if you let it. I don't think it's worth taking the chances with her anymore. There are other girls that you don't have a sordid history with. Let yourself move on and give one of them a chance. History has shown that things keep ending up ugly for you when you think you have a chance with this one.
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy