I dust the bedding and top the feed occasionally with food grade DE. It helps with parasite issues.
Is it possible some critter tried to snatch her thru the wiring and got a paw/claw full of feathers instead. Ripping them out of her body would make her swollen and red.
Is she laying well ...
Bare backs is usually from roosters hopping on and off, but can be plucking. Bare butts could be plucking/pecking. Any issues with mites or lice ??
Julie