Is she heartless? Sure. But leaving the keys in your car on private property isn't a crime. It's stupid, but it isn't a crime. Theft, on the other hand, is. So is driving without a license. The Evil Mother has one solid point. Based on the facts, the son and daughter essentially stole the vehicle and, near as I could tell, drove it illegally, and likely sped and drove recklessly. Both of which are also crimes. Should she have been watching her kid a bit closer, and not leaving the keys in the car? Sure, but that does not excuse their actions in taking the car and leaving the property to begin with.
Now, was taking that to court "right"? Of course not. That's a horrible thing to do to someone. And she has no case, as Judy indicated. Mostly because insurance and liability tends to legally follow the car, not the driver, unless it is stolen. She's likely had any claims revoked, if she had insurance to begin with, because the driver of her vehicle was both unlicensed and did not have permission to drive the vehicle. Regardless, you can't charge the girl who is deceased with the destruction of the vehicle, and you can't pass the blame and liability of the incident to her mother either.