OMG how sad.
We recently took in a Beagle that was in the same situation. She was so skinny it was scary. And she was losing hair on her body. I think that is from major lack of nutrition. When DH found her she was eating grass. When he got her to me, I was in tears. After not finding any owner to claim her, we decided to keep her.
Until I could get her to the vet, I gave her some of my girls home cooking and supplements. I think the supplement did her some good. She needed the extra vitamins. I used chicken, brown rice, sweet potatoes, green beans, etc. Then added the vitamins too. Believe it or not, she is doing great now. Hair has come back and well lets just say she doesn't have any ribs showing. We do feed her dog food now but I think the home cooking gave her a "jump start" on getting back in good health.