Question about being stuck with someone elses car payment, even though my name is not on it?

my father-in-law just ped away. he had signed for a car for his grown grandaughter about a yr. ago. her credit was so horrible she couldn't even co-sign. the honda civic cost her 21,000.00 at 430.00 a mth for 5 yrs... horrible!!! my husband and i were left with the estate and so today, she decides that she doesn't want the car/car payment and just dropped the car off at our house today. the honda dealership told my husband that 'the estate' is responsible if she doesn't pay. what on earth will we do? we cannot afford it and it is not our responsibility. she works two jobs, lives at home with her mom, no kids... while i am on disability with a small check and my husband doensn't make alot of money!