My Chicken lost all her feathers on her behind

[gggalaxy]

My chicken who I thought maybe molting seems to have only lost her feather on her behind. I was thinking it may be mites. I live in the PNW so we are in our rainy season and they don't have an area to take a dust bath. Does anyone have any suggestions?

 

[Kiki]

You could treat both her and the coop for mites using a permethrin based spray.