I hope that you have her isolated from the others. With chickens you have to treat themaggressively from the very beginning of symptoms because by the time they start showing symptoms they are very sick. If she dies (and I hope she doesnt) you should definitely get a necropsy done on her within 24 hours of death, if you have other chickens, because it could be ILT. Could be Coryza too. If you love the hen, and it sounds like you do, invest a small amount of money to consult with Peter Brown at www.firststatevetsupply.com. If I were you I would try to email him tonight and then call him first thing in the morning. He's not usually available much on weekends but if you flag
your email as urgent he might respond if he's around this weekend. He is much cheaper than a vet. At this point though self doctoring
by you is probably not going to do much unless you can get something like injectable Tylan. It is probably not ILT if she has lasted this
long. There are some avian vets who will treat chickens and I have found it worth it more than once to go to one. In the meantime, try
to keep her eating. Hopefully she still is. Give her warm oatmeal that's watered down a bit, or cottage cheese, or scrambled eggs,
mashed up fruit, anything she likes, because sick birds HAVE to eat, it's one of the most important things. If you know how to tube
feed her that is best although if they are very sick I personally think it stresses them out more to try this, but there are various opinions
about that. Disinfect anything and everything with at least bleach or preferably Oxine (you can mix it with water, I think it's 1/4 cup to a gallon). If she is still eating and drinking you might want to try some vitamins too.