Thanks for the details and pictures. She has missing feathers from her lower belly, so either another hen is pecking and eating her feathers, or she could be doing that to herself. I would watch for who is pecking them, and also compare her lower belly to other hen’s. Is it enlarged there? Hens may get an enlarged lower belly from water belly or a disease or condition. The bare skin makes it look a bit more prominent. Did she molt last summer or fall? Check her crop each morning before she eats or drinks when it should be empty and flat. It should fill up during the days as she eats and drinks normally. Hens can sometimes have reproductive problems, cancer, water belly, or crop problems as they age. I would maybe give her some Poultry NutriDrench 2 ml or another vitamin/electrolyte for a couple of days to give her a boost. Make sure that she is eating and drinking, and that her crop is empty first thing in the morning. Moistened chicken pellets and scrambled egg are good to offer if she is not eating well. If anything changes let us know. If she lays or seems egg bound let us know. Calcium citrate with D 3 is used if one seems egg bound.