I see some dried blood around her eye, so she may have gotten pecked directly in the eye, and it's now infected. Or it could be something more serious like Coryza or MG. I’d probably flush the eye with either saline or eyewash, wipe off any gunk/discharge with a warm damp towel, and apply an ophthalmic ointment to the eye (Terramycin is a great brand)repeat as needed.
Does this hen get pecked a lot? Is she showing any other respiratory-related signs such as sneezing, tail bobbing, coughing, rattle breathing?