Did you check for mites and lice????????
If she is eating the feathers she has a protein deficiency.
Have you ever wormed her?
Worm her and treat for mites and lice. Use Wazine as the first wormer and then isn a few weeks use the wormer Ivermectin. Sprinkle her with poultry dust and make sure it gets all the way down the feather shafts to the skin.
Get the book Tailfeathers recommended and up the nutrition for all your chickens. Give scrambled egg, cottage cheese, chopped greens, yogurt, chopped tomato, even a small pumpkin cut in thirds so they can peck at it. and small amounts of fruit. The fruit can cause diarhhea.
Don't give all at once. Give a treat a day.