She may be ill with something.
Mites require retreatment at 7 days to break the life cycle. Additionally, bedding and nesting material must be tossed to prevent a reservoir of mites in the coop that brings back the infestation. Coop must be treated with dust or spray (permethrin or other), and birds dusted everywhere but the face with poultry dust (or sprayed with poultry-approved insecticide). I use permethrin.
I would dust her and then the next day after the bugs have died, give her a dipped bath in shampoo and really clean her up. You don't want to do this until those bugs are dead.
Make sure she is spotlessly clean, and dust her again after she dries (blow her dry with hairdryer).
Be on the lookout for signs of illness. (Is she skinny? Diarrhea? Crop OK, for example.)
Your others should be dusted and redusted as well, because they can hide very effectively in the feathers. They move very quickly if they are the NFM.
I hope this helps!
Edited by ChickensAreSweet - 5/9/15 at 10:32am