Don't feel like you're bein' paranoid, 'cause this is reason for concern ... could be nothin' at all, but the eyes are an excellent entry point for viral and bacterial infections. I'd keep a good eye on her eye ~'-)
And, while you're at it? Check the rest of the flock for any symptoms of any kind.
I give Apple Cider Vinegar to my chickens on a very regular basis, as it can absolutely do no harm to your chickens, but often heads off diseases before they have the opportunity get started ... the rate is 4 teaspoons for every gallon of water (but NOT in galvanized metal containers), with the target pH being around 5~6 (slightly acidic). Empty and clean your waterer(s) and feeder(s) while you're at it, just as an additional precaution.
The tannin in the ACV helps to 'cut through' the mucus and coatings in the mouth, throat and intestines, helping them to better expel it, which improves uptake of vitamins/nutrients, which further boosts their immune systems, and also allows them to better absorb any medication(s) that you may be giving 'em in the near future. Do this for the next three days, and begin reducing the concentration each time you empty and refill their water (which should be at least daily, and more often if it tends to get dirty). And, after a few days w/o it, I begin the process all over again ~'-)