One of my hens has been looking progressively worse from spring until now. She was a beautiful 2 year old buff orpington, but she started looking ragged last spring. At first I thought it was mites. I read that some breeds are more susceptible than others and figured this is why she was the only one looking bad. I treated her and the coop for mites but there was no improvement. I talked to our vet, who has had her own flock and she determined it wasn't mites and suggested I keep watching for behavioral issues. Over the summer she got progressively worse. We never saw any signs of pecking or excessive self grooming. The vet thought it could be a nutrient deficiency, despite them being free range. We added kelp to their diets about 3 months ago and still no improvement. It has gotten to the point that I cringe when I hold her, and I think she'll have trouble surviving the winter. The shafts of her feathers are still there, but the barbs or soft full part are gone, mostly on her bottom, trail, and base of the wings/neck. Any ideas of what is causing this and how to help?