Looks like the beginnings of scaly leg mites. In the early stages like this they don’t cause problems but they can advance to a point where they are painful to the hens (and they cause some very ugly scale deformations as they burrow into the leg scales). At this early stages my suggestion is to slather her legs in petroleum jelly or something similar fora week for a month or so. That should smother the mites. You should also check your other hens carefully as it is very contagious. If it progresses and the petroleum jelly doesn’t seem to be working on its own oral ivermectin can be used. It can be purchased over the counter but you should consult a vet regarding dosage and withdrawal times for eggs (I know she isn’t laying now, but she will be soon!). It’s a fairly safe product it’s just not specifically approved for use in chickens so dosage/withdrawal times will not be listed on the label. It looks like you caught it early!
