My husband took an asl class. He attends all of the socials with me even though he doesn't know much. If your girlfriend is not willing to talk a class, she's probably never going to learn. It's really hard to learn on your own.
Here's a bit of advice that applies to all relationships--don't expect someone to change and don't fall in love with potential. My hubby was willing to learn because I'm going deaf. Not everyone is able or willing to do that. I married him because he's that kind of guy. You can find someone like him--someone who cares enough to learn. You deserve that!