Get some eye antibiotic ointment from the vet (vet will explain how to apply, it sounds scary but its ok really once you get the hang of it). Take a photo of the eye to the vet if necessary, saves the vet call out fee.
Orbenin is what I'm usually given for eye infections. They can easily pick up bacteria etc or get irritation from hay dust etc.
Eye infections are often highly contagious, so you would be advised to separate her (with a buddy for company), otherwise you could soon be having to treat the whole flock.