Hi, I'd like to help you with your question.
It sounds like it could be a couple of things. One, she is being truthful and doesn't want the relationship to be ruined by the rebound effect. Two, she is scared and is afraid she will get hurt again and three, she has relationship issues and this is her normal behavior.
Without being able to talk with her, I am only taking a guess here. But it sounds like she may have gotten scared and decided that she needed to back off. You mentioned that you were very compatible and that everything happened very quickly. This may have played a big part in how she felt. She may also been embarrassed by her behavior and felt the need to move away from the relationship. It could have been an overwhelming experience and she needed time to think.
Most likely, the best bet in this situation is to let her know how you felt about being with her and that it was a great experience. Tell her that if she needs space, that you will back off but that you would like to hear from her when she feels up to it. Then leave her be. If she wants to continue the relationship, then she will contact you again.
Without knowing her, I am not sure of what issues she carries into her relationships. She could have just had a bad experience in her previous relationship, or she could have issues that will affect her relationships until she develops the insight to deal with them. There is no way to tell which is why giving her space will help. It will give you the answer you need to determine if the relationship will develop or not.
I hope this has helped you,