Why dont try age old formulae?
"Have we met earlier? "
"Do we know each other?"
or even just a casual "Hi! "
how about to start, go up to her and talk to her. Don't worry, she won't bite... at least not for the first few dates.
Little crash won't be bad. Just walk into her. but not too hard, you know how I mean?
Or just something like: -Hi; -Hi; -Could you lend me....(something, eg. pen, calculator)
and then when you take that thing back to her: -Thank you; -No problem; -Bye... Er... Do you have something in plan this evening...
Only "Hi!" is not bad, but you have to know how to continue.
I would say the best thing you can do is probably just make you self a bit more noticeable. Once in a while just hang out with your friend in a spot you know she will walk by. Say hi to her when she walk by in the hall. Then start casual conversation with her.
Best of luck,
talk to her! even if she didn't tell your friend that she noticed you, you could have still said hi. good luck!