Answer:
If Sally is still a minor, she can disaffirm the contract and return the car to Bally. Contracts involving minors are not legally binding unless the minor reaffirms them once he/she is an adult or a parent also signs the contract.
In this case, Sally's contract is voidable by her and if she chooses to, she is able to void it. What happens after she returns the car depends on the state. Some state laws force Bally to return the money even if the car is wrecked. Other states have laws that require minors to return goods in good shape, and in this case, would allow Bally to deduct any repair expenses from the money he needs to return to Sally.