Why does she take long to reply?

There s this girl in school that I ve been taking to over snap chat. I know she digs me but she lags to reply. She told me from the beginning that her phone got stolen and she was using her iPad meanwhile so she couldn t reply because of the Internet and could only message me when she was at home. She messages me when she comes from school. And I understand but sometimes she messages me and I reply 2 min later and she replies 15-30 or sometimes even an hour after? Why is this does she not dig me anymore? Is she just to busy? Or am I just over reacting?