[TIGER 6]

Crilly,
Although it has been said before,I think what you are doing,as difficult as it is,is outstanding.
You have probably gone through all this,but a couple of alternatives:
.Get a loan from your bank on the car and have your niece pay you the interest by working in the summer,weekends etc.Have her pay the principle off over some time after she graduates and goes to work.
.Help her get a Federal or State or University student loan for the tuition etc.She is responsible for the principle after graduation and could help you with the interest if necessary during the 4 years.Just about every college and university has a wide variety of loan programs available to their students.
.If you have a house,a home equity loan with the same "deals" as above.

Hate to see you have to sell your car to do this very generous and selfless act.I hope she appreciates what you are doing for her.At the risk of sounding like I am lecturing,I think it is VERY IMPORTANT that you consider telling her this is 4 consecutive years-not take a year off to find myself after 3 years and finish later.I would also suggest that she have a little "skin in the game" herself to keep things focused and priorities straight,regardless as to how her college is being financed.I only say this after having "been there,done that."
Good luck,and again,WELL DONE!!!