Definitely do not throw the "BP" word around. I would imagine some people forget how much it intimidated them before they were diagnosed, but I'll always remember the day some 10 years ago when my sister suggested that I might be bipolar. It's a scary word! And most people who don't have the disorder equate it with "crazy".

That's probably where your gf is right now. I don't really know how you can broach the subject without alienating her. You could always buy a self-help book about BP and "accidentally" leave it out in view when she comes to your place (I'm assuming you have an apartment or a room in a dorm). It could be a conversation starter, especially if she assumes you're reading it for yourself.