What do her droppings look like? Coccidiosis is a possibility, anytime birds are moved to new ground they can be exposed to a strain they haven't been exposed to before, incubation from exposure to illness can be as short as 4 to 8 days. Being lethargic or sleepy, sitting fluffed up, not eating or drinking well are common symptoms, as well as runny or mucousy or bloody droppings (blood is not present with all strains). If in doubt at all I would start them on Corid right away. You can get Corid at tractor supply stores, rural kings, many feed stores. You can use either the liquid or the powder form, either will work. Most people find the liquid to be more convenient, but get what's available.
Dosing is 1 1/2 tsp of the powder or 2 tsp of the liquid mixed in a gallon of drinking water. Make fresh daily, make sure it's the only water they have access to during treatment, no puddles, ponds, etc, and treat for 5 - 7 days. The medication is very safe, it won't hurt them even if it's something else. I would treat them all. You can also give an oral dose to the one acting sick (or any others that do), dosing for that is here:
https://www.backyardchickens.com/threads/corid-oral-drench-instructions.1211991/
If she's not drinking well, you can also give her the medicated water orally several times a day until she starts drinking on her own.
Coccidiosis is very common, and some strains can kill very quickly, the sooner treatment is started the better.
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