A week ago?!?!?!??! She hasn't had anything proper to eat or drink in a WEEK!?!? That's not good. Just because she is separated from other chickens isn't good enough. She'll get dirt and bacteria in the wound. Bring her inside.
At first I was like 'what do they use for human skin grafts?" but then I realized you can't just buy synthetic skin, so the next option is real skin.That's the issue with leather, especially miscellaneous little scraps-dyes, treatments, chemicals, etc.
I'm wondering if you get some sort of skin from another animal? I know that deerskin is a thing that exists. Not saying it'd work, but maybe a different animal?
Cutting feathers will help keep the feathers and any dusty stuff (sorry i don't have a more scientific term) out of the wound, and will make for easier wound care. Clipping wings isn't painful for the bird, so I don't see why cutting feathers around a wound would be. The other option is to pluck...
Post pictures of the injury. Cut away the feathers so that you (and we!) can see it properly. Keep her INSIDE, in a warm place. Try offering her some scrambled eggs or wet chicken feed mash. Never let the wound dry out. Did you say that when she drinks, the water comes out of the injury?