How long ago did she last lay an egg? As I had posted in your other thread, from her symptoms and appearance, I would suspect a reproductive disorder. It is an unfortunate, but a common problem in hens. Salpingitis, internal laying, egg yolk peritonitis, ascites and oviduct cancer are some of the common ones. A year ago between Christmas and New Years during a cold snap, I lost 4 older hens to each one or a couple of those illnesses, and I confirmed it with a necropsy at home. It is never easy to deal with, and what I do is to try and keep them eating, and as comfortable as possible. Usually, they like to be with their flock as much as possible, so I let them until they start to be picked on. If they are picked on or appear to be suffering, then I put them down. Sorry about your hen, and I would try to see a vet if possible, or try antibiotics.