My pullet Nawa is acting a bit odd. She is very slow and sleepy looking. I gave them cooked rice as a treat and they usually go crazy! She just calmly ate five grains of rice and stopped. She sat alone and looks very tired. Her crop is full of water and not much food. Her stool is green with white. I got her on July 22. She'd also breath through her mouth sometimes but it's cool today and she drank water.
Lethargy can be so many different things. The best course of action, if you can do so, is take her to a vet for a check up and to have lab tests ran including a fecal.
Otherwise, you have to do a lot of "best guessing" and possibly over treating or wrongly treating until something works.
It could be a number of things.
Since you got her fairly recently, and she isn't sneezing or bubbling at the eyes, my first guess would be to treat her for coccidiosis.
Although her poo isn't diarrhea or bloody, she could have a lurking infection because she hasn't adapted to your soil yet (where the coccidia protozoa live). Not all coccidiosis produces bloody diarrhea. Often the first and only symptom is lethargy...huddled in a quiet corner, fluffed. New birds will often exhibit this after the stress of a move.
The treatment for that is Corid. You should treat all the birds as she would act like an incubator for all of them.
The other possibility is a bacterial or viral infection, or she may have a worm overload, or even external parasites.
Do a careful check at her vent to look for creepy crawlies and egg nits. Look through her poo for any sign of worms (often you won't see any unless you do a fecal float).
You could then dust her with Permethrin dust, repeating in 7 days. It would be a good idea to treat the whole flock as bugs travel from bird to bird.
You could worm the whole flock as if one has it, generally the others will too.
If it is viral, it will run its course. If it is bacterial, she will need antibiotics.
But I would try first a vet, if not that, then Corid and dusting with Permethrin.
Also give her some TLC with protein boosts such as scrambled eggs, yogurt, and apple cider vinegar (raw with mother) in the water (only plastic containers).
If she doesn't perk up after a few days of Corid and/or TLC, I would look at other issues.
I'll link a poultry checker below to help you sort through her symptoms and possible causes.
Good luck with her. I'm sorry your hen isn't feeling well. Hopefully she'll rally soon.