Dude, you move too fast it's your problem... A chick with anxiety issues is bad. All these kind of relationships are a real waste of time. They'll only last a couple of weeks. Find someone who wants to talk with you at the end of their busy day. And as said by the person above ^ have some consideration.
I think its way more his fault than hers, just cause she has anxiety issues and is crazy busy with school doesn't mean she needs someone in her life causing more stress just because he hasn't gotten laid. Maybe she doesn't want to talk at the end of the day because she needs time to do school work and sleep. Instead of ignoring her, how about you man up and call if you really care about a relationship with her.