Is she still in the wrap or have you taken it off? I don't know everything about chickens, this is only my second year with them but the black could either be the bruising or the skin dying if there's a lack of blood flow to the area. Is it oozing or dry? She might be on her back if you still have the wrap on her because she doesn't like it. Continue to make sure she's eating and drinking. I wouldn't wrap her wings unless you really think they are broken because keeping the wounds covered could cause infection and it's better to let the wound air dry.