Backyard Fowl Keepers

Sometimes a cold environment can stress out hens and make them lethargic. If it's been very cold where you are, I'd try giving her a warmer environment to see if it helps. It's also possible she's having trouble with molting or just stressed from the season change.

It sounds like she might be dealing with something like Marek's Disease or possibly a crop issue. A full crop should not stay empty, so I'd definitely take a look at that. If she's still drinking, that's a good sign, but it might be worth checking for any other symptoms like swelling or respiratory issues.