Welcome to BYC. Worms or coccidiosis could be a cause for her illness. How are her droppings looking? I would probably get some Corid (amprollium) a cattle medicine, and treat her and the others for possible coccidiosis. Dosage is 2 tsp of the liquid Corid, or 1.5 tsp of the powder per gallon of water for 5-7 days. Then give her some vitamins and probiotics for a couple of days, and then worm the whole flock. Valbazen and SafeGuard liquid Goat Wormer are very good. Also, look her over for signs of lice or mites. And you may want to feel an inch inside her vent for being egg bound.