Hi
Hot2Pot could be right, eye worm or coryza are 2 possibility's " if she has a cheese looking discharge it is most likely one of these.
But she may have just been pecked or scratched it, or got some dirt or dust in it.
Get some Iodine and water it down,and use an eye dropper to drop some in, and keep your eye on her, I recently had a young Pullet get her self trapped behind The Broody boss hen in her nest box and her eye was all weepy and puffed right out, I gave her some antibiotics and the eye drops, and kept her separate, and by the next day her eye was nearly normal "just ever so slightly swollen, and the following day she was back to normal.
Hope this helps
Cheers
Bill