Not sure looks like some kind of mite I have been treating with permetrin problem started about
month ago I started treating 3 weeks ago it doesn't look much better.
It looks like she is being overmated. Do you have a rooster? If you do, get her a hen saddle to protect her feathers, and they will grow back. You can also give them some mealworms once a day. It gives them some extra protein which helps them regrow their feathers faster. Key word: SOME, and ONCE a day. Too many mealworms can throw off the nutritional balance that they get in their feed.
In the other two pictures you posted, she had just taken a dust bath, so her butt fluff was full of dirt. Otherwise I think it looks fine.
She may very well have mites. Look closely at her face; can you see any bugs crawling around? Check around her vent as well. Lice like to lay their eggs around the base of the feathers. Take a close look at the eggs in the nestbox. If there are any mites hanging out in the boxes, you may catch them crawling on the eggs.