So what went wrong?

They did not do a proper risk assessment, did not understand the environment they were going into. They made bad decisions against all of the existing indicators that they should not go to that area. They did not know the limits of cell phone coverage. They did not know the way back out once they did get stuck. They had no plan for such an eventuality. Overconfidence that was entirely unwarranted in this case.

They were not prepared with the proper equipment to extract their vehicle when it got stuck, and I am sure they were lacking in many other times most of us would consider essential.

They had no alternate means of communications, did not tell anyone where they were going or when to expect them back.

While she did have stamina and perseverance, she had reached the limits of that and was not even able to search the area around her to find the resources necessary to survive. Her physical fitness kept her alive, but it would not have for much longer. She had exhausted the one resource she did have.

What they could have done (other than just not making such a bad decision):

They had shelter (their car) which could have been improved significantly. With a fire they could have stayed warm and had plenty of water; which means they could have survived for up to about 3 weeks. With some food stocks that could have been extended for much longer.

With a fire they could have signaled for help. The Rangers in the parks are always on the lookout for smoke, and under decent weather conditions that smoke could have been seen from a great distance, drawing attention and investigation.

They could (and should) have left a trip plan with someone.

They could have invested in a satellite communications device.

They could (and should) have avoided the off limits areas to begin with.

They could have stayed on a main road which would make it less likely that they get stuck. This would also have eased the walk out for her, and the ability of rescuers to find them.

As in many of our discussions in this forum, there are some basic things that anyone should carry in their car, more for extreme weather conditions and travel in remote areas. We have numerous lists and recommendations that anyone out there can read at no cost. There is little entertainment value to the mundane task of being properly prepared. As Peter Kummerfeldt so accurately describes it: If you are prepared, the situation is an unexpected or unplanned night out and does not become a survival situation.

as has been stated, the simplest good preparation and sound decision making will avoid bad situations to begin with. An ounce of prevention is worth a pound of cure, though it is not as exciting.