From the pics and the posts I would say make a deal with the owners to haul her right to a vet and put her down. You pay the costs, they surrender the horse. Without alot of expensive vetting and long term care that mare will probably never have the quality of life or usability she should. And if you do manage to get her rehabbed are you prepared to keep her as a pasture muffin for the next 20 years? OR ensure her future if you can't? Sorry. Good Luck!

For the great majority of mankind are satisfied with appearance, as though they were realities and are often more influenced by the things that seem than by those that are. (Niccolo Machiavelli)