I too know this area pretty well.
The majority of the Northern Tracks are doable with a car, I know a group of Mokes that drove from East to West through the entire park without issues (but I guess if one of them got bogged 2 people could lift it out). I've seen falcon utes drive the Birdsville. So the choice of her Vehicle is not the issue.
But issues can occur without warning, doesn't take much to get a car/van bogged. (I dragged two cars out of soft sand less than a metre from the side of a bitumen road on the way to Adelaide one day as they both had stopped for a leak. I was the first of several passersby that had anything on board to tow with). So you don't need to be remote to get bogged.
The real issue is how prepared are you if travelling remote and alone.
Did this traveller have a map of the park (generally found at the entry into the park). This would of helped significantly in the choice of shortest track out of the park.
IMHO I think she did the right thing in walking out of the park, given no-one knew she was there, and the lack of other travellers this time of year, and with the right precautions of water, food, shelter and PROPPER footware, and walking the cool times and resting through the hot times, it was survivable. (Remember surviving with sore feet is better than dieing without trying) Did she leave a note with her van telling of her walking out in case a vehicle came upon her van from the opposite direction to her walking?
What would of happened if she stayed with the vehicle, no-one looking for her, drank all her water, and still no-one came along, then she would have no escape means.
If it was me out there, and I died under a tree trying to get help, then great!, better to die out in this beautiful country than dieing in a nursing home in front of a #$%&* TV.
Out of all this I believe that she should of had an EPIRB as a minimum, whether in or out of mobile range, flat phone battery, duress, whatever, at least someone is alerted to her trouble no matter where she might be.