Curiously, on what legal authority are you telling the OP that she would have no defense if sued by the "victims of the hit-and-run accident"? Even presuming that the facts presented here would admit of the application of the doctrine (which IMO they do not) where do you find that it even applies in Tennessee? I can't find that it does. And per chance that it does not apply in Tennessee then common law principles would obtain in which this particular form of vicarious liability does not exist.
And even if the doctrine were administered in Tennessee, your so-called victims would be faced with a difficult burden of refuting evidence that the vehicle was being operated by its legal owner and disproving that the OP had relinquished all legal claims to its ownership. How faced with the terms of the agreement ratified by the OP can it be said that the operator car wasn't its legal owner?
I don't see a juror or a judge imputing the operator's liability to her. Not under these circumstances.

