Your hen looks like an older pullet or a mature hen. If there's no discharge it can be infectious laryngotrachetisis (common respiratory disease) influenza (rare), or Marek's disease (common). This is all according to my "Chicken Health Handbook" by Gail Damerow.
I'd isolate her so that if she has something contagious it is caught early and so that it doesn't spread to your other birds.
Good luck with treating your hen.