Why did this girl start ignoring me?

You sound super sweet, and I'm sure she wasn't weirded out or anything by you looking away. That's a totally normal thing to do when you like someone. If I were you, I would try to initiate some real conversation with her. Not on twitter, twitter is really just an excuse not to talk. Even something like facebook chat would be more effective, because you're having a real conversation back and forth. After you do that, wait and see how she responds. If she seems interested, great! Keep chatting and then build up to talking in person. If she doesn't seem into it or want to talk to you, then just let it go. You need a girl who likes you as much as you like her, and if she's not that girl then you have no reason to be upset over her. Good luck!