What does her poop look like? Is she eating and drinking? Are the others picking on her? Do you have more than one feeder and waterer available? I would try to get her eating something by taking her aside, and offering scrambled egg, wet chicken feed, and vary that with a little tuna or canned cat food. A chicken vitamin such as Poultry NutriDrench 1-2 ml daily for a few days would be good. Or 1/2 vitamin B complex tablet crushed into a little food or water would be helpful and might increase her appetite.
If she is not eating, I would start some Corid in her water to treat her for possible coccidiosis. That is found in feed stores. Dosage is 2 tsp of the liquid or 1.5 tsp of the Corid powder per gallon of water for 5-7 days. Symptoms of coccidiosis are lethargy, standing puffed up, no appetite, and runny droppings.