you could email her back and ask her what she wants to talk about. then you'd be a bit more prepared or could tell her if you're not ready to discuss certain things. i think it might be good for you to talk to her since you say you don't understand why you guys broke up. it sounds as if that is haunting you a bit and a conversation could shed some light. or, starting an email dialog is another way to talk if you want a bit more distance.