If a girl that you dated in the past want you to pay her back for everything she ever did for you and is threatening legal action but has n binding contract between both of us what could happen?
Without more details, it's hard to say what might happen. But one possibility is that she files a lawsuit. If so, you have the opportunity to defend the lawsuit, and tell your side of the story to the judge (or jury).
It would depend entirely on the facts and evidence in the particular case. Without that there is no way to even guess at an outcome.