I have found that most girls/women respond quite unfavorably to being called "hey you".
Seriously...find out her name. Surely someone you know knows her...or at least one of her friends. If you don't talk to her, you'll drive yourself crazy thinking about her, fantasizing about being with her, only to be disappointed. Been there...done that...they were out of t-shirts though.
Strike up a conversation. Talk about what you're studying. Work on a project together. Do something to start a dialogue. You'll be amazed at how easy it is once you get it going.
"Purgatory's kind of like the in-betweeny one. You weren't really shit, but you weren't all that great either. Like Tottenham."
I'll try being nicer...if you'll try being smarter.