First: Don't listen to a bunch of 15 year old guys on the internet that would personally love to tell their own parents to f off, and therefore think thats is what you should do.
Second: If her parents are paying for the tuition, I wouldn't create waves. Your girlfriend may not be live under their roof directly, but they are still paying to put a roof over her head. While telling her mom to f off sounds refreshing, if they cut her off you have to live with the fact that you messed up your girlfriend's life. If the relationship doesn't work out, how would it make you feel if you drove a wedge between your girlfriend and her parents. If you must tell tell them, be civil about it.
Third: This is the easiest, Torrent some old Loveline episodes. Adam and Dr. Drew are great on life advice.
Forth: Get therapy... This may sound harsh but almost everyone could really use therapy at least during one point of their life. Your dad has been out of your life, you say you have an open relationship with your mom, but you admit you don't talk often. You are lesbian in a not very accepting world. Your college should offer free consoling/therapy to students... TAKE IT! What could it hurt and it won't cost you anything! I've been in therapy, and my gay brother has too. I'm glade I did it, it didn't rock my world, but it did make me feel better and help me get more organized with my life. Your internal compass sounds like it is spinning like crazy, if you don't take some time to work on yourself, even if you could be open with her parents, that isn't going to solve any deeper issues in your life.