If she is alert enough to eat and drink, that makes a difference I think. If she's just sitting with her eyes shut constantly she's pretty far gone and preoccupied with her misery. If she's alert we don't really know how much pain she's in. Cham ribs are more cartilege than bone but do heal. She's exhausted and weak because of poor nutrition. A good diet and supplements might do a lot in a short time. An animal suffering so much that it can't or won't eat has lost interest in life. That's when I would euthanize.