Hi,
I don't see how the animal has any chance of coming back from that kind of damage at all.
Even if it managed to avoid the infections and survive long enough for scar tissue to form what range of motion or sensation could it realistically have?
It would be a rare vet willing to try and help this animal do anything but die pain free as quickly as possible.
Home/ no treatment for any animal with that severe an injury is the absolute opposite of kindness.
I don't doubt the intentions she had were good but the end effect is horrible in the extreme from the animals point of view.
However I can see a rat being able to inflict that kind of damage quite quickly - overnight would be plenty of time for a determined or hungry rat to do that kind of damage.
I hope she comes to her senses quickly or someone calls the authorities - sitting watching it suffer is no answer I could live with and call myself human let alone an animal lover.
dr del