it was her mom's car and she can sell it if she wants too. If she only bought it in the first place to motivate her daughter to get a drivers license then mission accomplished. And selling it motivated her daughter to get her own car.
actually if my girlfriend's mom did that, i wouldnt be upset I actually may thank her for teaching her a lesson that without such could of given me a headache. Self Sufficiency is a good thing even if it takes "tough love". I realize its possible she may of done it all out of her own selfish wants, but still i dont see the bad surmounting the good.