She probably has black ear or it's called leather ear. It's caused by her ears being cold and you need to keep the ears warm by rubbing them, keeping her in a warmer room. Her hair probably won't grow back to any length but it's not life threatening. I have a couple of dogs that had it but I keep the ears room and try to keep them in a warmer area of the room. The sun really helps keep them from getting black ear and out of cold damp areas. I hope this helps and please get her to a vet to check her health from being so skinny
Donna Bird
Brooklynn's Yorkshire Terriers