If the eye hasn't been injured or received an insect sting, she may have a respiratory disease such as mycoplasma (MG) or coryza. I would look for any marks around the eye from pecking or a sting. Do you see any nasal drainage or any pus in the eye? Does she have any chest rattles or cough/sneeze? If you believe it to be a respiratory disease, oxytetracycline in her water may be good to use if she is drinking well, or Tylan 50 injectible if she needs shots. Here is a good link to read about respiratory diseases: http://edis.ifas.ufl.edu/ps044