I agree, it sounds like she may have Ascites. Draining can be done if she's having difficulty moving about, labored breathing, etc. A mentioned, it's a temporary measure, but can give a hen comfort for a period of time.
When was her last egg?
Feel of her abdomen below the vent between her legs for bloat or fluid.
She may be starting to have some reproductive issues. These can cause some of the symptoms you see.
Offer supportive care. Vitamins a couple of time a week, see that she's eating/drinking. Look...