So if I've understood this right, you're both attractive young women in the same classes, but you're out as bisexual and she's presenting herself for the most part as straight. And maybe she is, but she seems drawn to you in some way or another.
So really, if she's interested in you, it's up to her to let it be known that she's into you, in a sexual way. You've done the brave thing of being out, which makes it easier for her to figure you out and know if she might have a chance or not, so now it's up to her to do some of the work and go after you. Or if not that, then letting the world know she's bi (if indeed she is), so that you can safely proceed to pursue her.
As for what you can do, I suggest you play it cool. In my opinion it's not enough for her to be sitting close to you, or staring at you. That's too passive. She's waiting for you to do something, but she hasn't even got the guts to out herself (if it so happens that she is bi). That's not fair on you. Expecting you to make yourself vulnerable by approaching her first, when she has her safe straight persona to retreat to at any time. If she wants you, she's got to out herself first.
As for now, I'd just ignore her. (unless of course you're really hardcore and invincible and willing to chase after her and risk rejection from a straight girl).
