Was your flock vaccinated against Marek's?Another thing there is no bloody poop. Her eyes or nose are not seeping fluids and no other physical symptoms other than being lethargic. I wet her food and if I can keep her awake she eats it. Water only by hand though.
This is not a case of coccidiosis so you don't need to continue with the Corid.
Does your flock free range? Could they have gotten into something toxic?