We have several worrisome data points. It was posted "she was in no condition to drive". Now we learn she was given incorrect driving instructions. I will also very respectfully point out this is a woman in her 50's who is carrying a significant amount of extra weight. I respectfully point that out to emphasize should could have had a medical episode in addition to an accident. (And/or).
I agree it is imperative that this woman be found right away. TRUCKERS are your best bet here. Get to one of the truck stops and ask for help. They are good people and will get the word out. It's highly likely one of them spotted her car, or will.