You shoudl immediatly write a letter to your freind describing the deal and asking her to write back as to why she wants to change it. If she signs the letter backto you, it with a copy of the letter you wrote may make your verbal agreement a written one. This may allow you to keep the car for now, and to get some compensatin if she takes it back. You may have to go get new financing to get to keep the car, as the letters may show that the new agreement is that you make payments to her until you can get financing, not till you get the financing you want.
Good luck
