Payment Authorization For Sale of property

My sister was authorized by her father in law (seller) for receiving payments for the sale of a property to my sisters friend ( buyer). Her friend paid a downpayment to my sisters father in law when the three of them got together to discuss about it. No papers were involved just word of mouth. Every month my sisters friend would pay my sister for the balance. A year had passed and my sisters friend fully paid for the property. Now the deed of the property cannot be given to my sisters friend as the owner said the buyer only paid the downpayment. the buyer is insisting that the money wasnt given to the seller by my sister which is true, reason why the deed will not be transfered. the buyer will be filing a case against my sister for theft and estafa. The seller didnt even ask after receiving the downpayment why the buyer isnt continuing his payment for a year. They also dont have any evidence that the money was not given to the seller. what will happen to my sister? Can she just pay for the amount and not be imprisoned?