x2. My first thought was vent gleet IF there's a putrid odor enaminating from the rear end, not avian TB. Ecoli bacterial infection could be the problem as well. Only a necropsy will tell what's going on.I seriously doubt that your chicken has TB from the symptoms you describe. Avian TB is transmitted usually by wild birds. It IS dangerous, because it can spread to humans who are immunocompromised such as AIDS patients, young children, but it also can spread to cattle, horse, dog, etc. With any chicken necropsied to be found with TB, the whole flock should be destroyed. In this case, it could be anything in the world wrong--coccidiosis, enteritis, kidney disease, and numerous other diseases. In her case since she is going on three, you may want to investigate internal laying or egg yolk peritonitis as possible causes. Most sick chickens will eat a scrambled chopped egg. Here are some links to read about egg yolk peritonitis and internal laying, plus one on avian TB for anyone else interested:
http://www.chickenvet.co.uk/health-and-common-diseases/egg-laying-issues/index.aspx
https://www.backyardchickens.com/t/526089/egg-yolk-peritonitis
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3135220/