Welcome to BYC. Do you know how old the chicken is? Pictures of her and her poops are welcome. I would examine her whole body and look for any enlargement of her lower belly between her legs. Examine her vent where the eggs and droppings come out of a common junction, to make sure it is clean and not caked with poop or maggot larvae from flies. Also check for any moving bugs (lice or mites) on her skin under the vent and elsewhere. Her crop in her right chest is the sack where her food and water are stored after eating. Feel of that to see if it is empty, full, hard, or puffy like a balloon. It should be full during the day, and empty by the next morning before she eats. Smell for a sour or bad odor from her beak. Feel her breast bone to see if it is prominent if she has lost weight. Hens can commonly suffer from reproductive disorders after 2 or 3. Molting which occurs in late summer, can cause them to lose feathers, look scruffy, and stop laying for a month or two. Try giving her water and some wet food, and perhaps a bit of scrambled egg or sunflower kernels. Water is most important, and Poultry NutriDrench given orally, is a good boost of vitamins and electrolytes.