Does mom have legal rights to my car if she is co signer?
If the loan is as yet unpaid, then yes. As long as her name is on the loan, she has the right to weigh in on the financial future of the car. She has a vested interest in any actions of the vehicle which may decrease it's value. She also is entitled to oversight of any cash generated through the sale of the car because default of the loan will effect her financially.