It could be a variation of reasons. For one, it could be that she panicked because she realized she was getting close to someone and she didn't want to be in a friendship like that. Another plausible reason is that she didn't want to talk anymore, therefore the easiest any to ensure that is to block you so you can't ask questions. There are also many other reasons, but I wouldn't take it personally unless you really did do something that was overtly wrong (for example, pressuring her to do something she didn't want to do).
