I think there could be a good possibility of your chicken having a reproductive disorder which includes internal laying or egg yolk peritonitis. Symptoms can include not laying or irregular laying, loss of weight in the breast area, sometimes an enlarged spongy or tight lower belly, loss of appetite, a reluctance to walk ber far preferrring to sit or lie down, and sometimes odd walking including like a duck or more upright than usual. Antibiotics early in the disease may help prolong life, but will not cure it. If vet care is available, you may get some testing done to rule out other problems. I don't see any evidence of vent gleet which usually includes a scalded vent area.