Can she move her legs at all? You may want to get her up into a chicken sling to keep her cleaner and make it easier for her to eat and drink. Here is a video:
Compare her lower belly with the other hens to see if it is enlarged. Look for any lice or mites, and irritation from lying down so long. Do you see any evidence of injuries? I offer a scoop or small cup up to the hen’s beak to get them drinking and eating. Wet chicken feed with lots of water, scrambled bits of egg, a canned cat food can be offered in small amounts to get them eating and drinking.