You won't know for a while. You seem pretty knowledgeable about rebound relationships. They tend to heat up really fast and move really rapidly. They can cool down just as rapidly. You won't know if that happens or not until after she is completely out of the other relationship. All you can do is wait and see what happens. The end of relationships is very painful, and sometimes we latch onto people to make ourselves feel better. I suspect you know that. Sometimes, we latch onto people who aren't right for us and we ignore those differences because we need the support. When the stress is past, then it becomes a "regular" relationship, whatever that means. I'm not sure you really have to do anything differently.