You may want to take Shadow to the vet for a checkup. If all the young dogs just started attacking her out of the blue, they may have sensed her being weaker from sickness. Or it could just be older age. If she was previously alpha, she is probably getting challenged for that position.
Its scary that your dogs have pack behavior like that. I realize it happens in large groups of dogs, but they should all be looking at the humans as alpha. They should listen to you if you tell them to stay away from Shadow. I would keep Shadow but not leave her unsupervised with the rest of the dogs. I would also work with the other dogs individually to build stronger bonds with the humans than the other dogs. Their own species is so much more interesting, so when you have a lot of dogs, you really have to be careful.
Shiloh, Reece, Lolly, Skylar
and fosters Snickers, Missy, Magic, Merlin, Maya