I know it is a hard thing to do right now, but you have to try to put these "what if" thoughts out of your head and let them go. There is no way you or any of us will be able to know what she is thinking.

You mentioned that you don't know why she left you. That can make finding closure more difficult. I think you should wait and see what she has to say and then bring up the end of your relationship to try to get some answers. Do you think she is someone who will be willing to talk to you about that?