ThanksThis is one of the few times it's relatively simple to take a shot at a diagnosis from just a single photo and zero accompanying information. Your chicken is a likely victim of Coryza. If there's a bad smell around her head, that would be further evidence of this respiratory disease.
Treatment consists of administering an oral antibiotic, expressing the pus from around the eye, and treating the eye twice a day with either Neosporin or Terramycin eye ointment.
It looks like this has been going on a long time. There may have been some pecking. The area around the eye looks like it has scar tissue. I would try to clean up the eye as best you can with saline and use some antibiotic ojntment into the eye. Is the eye still visible? What symptoms does she have?