It looks like she was a hard broody before you got her. I have had some that looked like plucked turkeys from chin to vent for a long time. I would go easy with high protein, too much can cause other issues but adding some is good. You could try giving her some vitamin E gel caps broken into her food. Vit E is good for the skin. Flax is also good in small amounts. The browning of the feathers is normal when they are aged.