Hmmm... well, this might be a bit rude, but it's just a suggestion bro. You don't have to take it. And if this offends anyone, I'm sorry... it's meant to be funny. But I'm no comedian.
So in the wee hours of the morning, on your way home with her, act like you're sleepy and say you feel tired. Ask if she doesn't mind if you stop for a while to rest. Take her to a motel.
Two things can happen and the other is that she will stop getting a ride with you. The other, well, bahala ka na, you're on your own.