Have you looked over her skin for evidence of mites or lice? Did she come from a hatchery, or was she hatched locally? If there are no bugs on her, she could have something else bothering her such as pasty butt, or something in the bedding is irritating her. What type of bedding are you using, and do the chicks have plenty of room. Are they too hot or too cold? I would try to distract her by sprinkling some feed crumbles around her feet to peck at, make sure she is drinking water, and you could also apply some menthol ointment (Ben Gay) or some Vicks to her bottom. Pasty butt is constipation brought on by dehydration, and with daily gentle washing and a drop of vegetable oil on the vent opening, it usually subsides in a week.
Be cautious using DE or Sevin on a chick. Both can affect the lungs, and Sevin is probably too harsh for chicks. If you need something for lice or mites later on, then permethrin dust or spray is probably a better choice.
Edited by Eggcessive - 9/29/15 at 11:48am