Gosh hard to say what the scaly base of the feathers would be, you could spray some permethrin spray; used horse fly spray for a few hens I bought home with lice, worked brilliantly. Spray under the wings, on belly by vent, and base of neck, anywhere you see the scales. Make sure to get it at the base of the feathers, don’t soak her though. If you notice the scales clear up in a few days you can assume it’s mite or such. Repeat treatment in 2 weeks.
Sometimes you have to play around with treatments to see what works. If you had a vet that could use a microscope to check sample of the feathers they could tell right away if it’s mites or such.
Here are a couple feathers I hauled off the birds with the lice. You can see the egg cluster at the base of the feather which is why you treat again after 14 days - tie eggs will hatch by then but the baby lice won’t be old enough to breed.
You might want to pluck a couple feathers and see if you can see anything with a magnifying glass.
Also ivermectin will kill lice and mites and same thing treat in two weeks.
