Man, this is what I suggest you do. It is somewhat simple, but it requires you to step up to the plate.
1. Marry your girl on paper in the U.S.
2. Apply for her
green card as as soon as you are married. Use a
lawyer!
3. When her status goes out in May next year, she will by then have her green card.
4. Once she does get the green card, which should be way before May, she can quit her job on the spot. But not before.
5. Step up to the plate tonight and ask her to marry you!
6. Tomorrow, go and get the marriage certificate, go through with the ceremony and hope you made the right choice!
Good luck!