What do you do when your dog is being eaten by mange and wont eat any food and is so weak she cant stand up ?

i have a dog that was a stray . when we found her she was being eaten up by mange and we tried to nurse her back to health. she got better but then it got colder outside and she began to get worse. she has many open sores and her body that wont heal. we give her baths in hydrogen peroxide and borax every week or so. she has gotten to the point where she wont eat anything and i still think she has mange. she also is extremely weak and she has been laying in a little pallet of blankets on the floor for at least 2 to 3 days. she is horrifyingly skinny and i don't know what do to any more. im afraid she will die from hunger or sickness. please someone help me!