Oh, and do you have any buttermilk or powdered milk? These products can be used to slow down the effects of the Coccidosis. If you have some or can get some, give either item to your birds until you can get Corid. This will help them survive.
The protozoa that cause Coccidiosis are always present in a chicken's digestive system, in small amounts. It can be found nearly everywhere, in wet litter, droppings, etc. If a chicken is suddenly introduced to a new strain (there are nine types of Coccidiosis, all infecting different parts of...
I don't think that you should separate her. She would be lonely, as would the other ones. All of them have probably been exposed to the disease, so treat them all.
She could have Coccidiosis. This disease causes droopiness, sleepiness, lack of appetite, listlessness, lethargy, and sometimes bloody diarhea. It can kill quickly, so I'd get some Corid (Amprolium) as soon as possible. Corid is sold for cattle and livestock, but is a treatment for Coccidiosis...