Co-Signing for a vehicle?

I recently co-signed for a thought to be friend on a car. Everything was great up until this point. After I co-signed everything changed she became rude and even assisted her spouse in robbing me. I have called the finance company and they told me that I could not remove my name from the car until the car was paid for. They told me that since I owned the car as much as she does that I could take possession of the car. I do not want to take the car from her because she did trade her old car in on the new one and taking the car will leave her without a car at all. But I can't understand why this has happened. She has not paid anything on the car other than the trade-in which they only allowed her $1000.00 for it. I guess that she was using me because her and her spouse wanted to buy a car but no one one would approve them (even the buy here pay here car lots). So I have like two options (1) take possession of the car and finish paying for the car or sell the car or (2) leave it alone and hope that she keeps insurance on the car and actually pays for it. Anyone know what should I do? I know that I should not have co-signed for her in the first place but for some reason I always get in trouble trying to help others. Please tell me what I should do because I have no idea-- but it will not quit bothering me.