My leghorn did that, she pulled out all her feathers from vent to breast so she was 1/2 nakey. She was trying to set on eggs, go broody. She would sit on nest and only move off if I made her and collected eggs. After no eggs she would run around doing her crazy chicken things. Not all the eggs are fertile yet as Roo still trying to perfect his technique.
For your hen I would make sure she is eating and drinking. Or put her in a wire bottom cage for air to get to her bottom to break her from being broody 2-3 days.
For my hen I checked her over for mites/lice didn't find anything. Sat and watched her to make sure others weren't pecking her feathers out. They had also been wormed in January. She would stand in nest and yank the feathers out, even pin feathers. The feathers were tucked into the nesting material. The other hens would lay in the nest, arrange the material and sometimes eat the feathers.
She kept trying to be broody for quite awhile. I put her down when she was severly injured from a rat or weasel that got in the coop. The Roo Dino and 3 others were injured not badly chasing it out, fur was stuck in their claws. They only had small scratches compared to the broken dislocated wing, bites on thigh, and broken bones in the foot of leghorn. She put up a heck of a fight protecting the nesting area.
Miss her crazy antics, she taught me a lot about caring for sick, injured, vent gleet, sour crop, foreign object in crop ( was a piece of domed plastic about size of a nickel, no idea what it was) egg bound, she taught me that and more. Too bad she was the crazy hen of the flock.
