Are the pin feathers just in one area, like she has been pecked by the others? Hopefully, she is just completing her molt, but keep an eye out for others picking on her, which can happen to lower pecking order chickens. I have noticed occasionally, that a chicken that age can show symptoms of a reproductive disorder. They may stop laying, lay thin shelled eggs, eat very little and lose weight through the breastbone area, and be a bit lethargic. Some chickens with internal laying or egg yolk peritonitis can have a swollen lower belly, sometimes with fluid or egg masses inside. Many times, treating a hen like yours, has to be done by ruling out everything else. Lice, mites, worms, poor immunity to coccidia in the soil, crop problems, and reproductive disorders are many of the common things to look for or treat. You can sometimes talk your regular vet into checking a few droppings for cocci and worms. Vet care is good if available, but sometimes too expensive for many of us.
