you have to look close at the feather shafts Louly.... I cant tell with the images, but I think I see little dark gray spots of something?
I thought the dots were scars from missing pen feathers.. oy vay. but I am new to this. She is still laying and is the only one with this problem... better work fast I suppose.
Linda, do you have a rooster? It looks like it could be overbreeding. Dominant hens will do IT too. Looks like she is being picked on. Get her a jacket.
When you treat for mite/lice, you need to treat the whole flock and the coop. I've had northern fowl mites here and red roost mites. Both were easy to see when you look and no chicken ever had feather loss like yours, even with a pretty bad infestation. If it's not a rooster, somebody is pulling her feathers.
X2. I had white chickens with lice but it was super obvious.