Divorced, car in both of our names she is not making payments. What are my rights?

I am divorced and my ex has a car that is titled and the loan is in both of our names. She is supposed to be making the payments but is late every month which is affecting my credit. I have enough money now to payoff the loan but want to ask her to make the remaining payments to me, is tha legal? If she says no what are my rights or do I just have to payoff the car and not be reimbursed for that payment from her?