Swollen shut eye
Does she have any noisy breathing, nasal drainage, sneezing, or other respiratory symptoms? Is there any pus or drainage in her eye? Could she have been pecked around her eye? Have any other chickens recently been sick? She may have an eye infection, or she could have a respiratory sinus infection. I would clean her eye with saline, and look for anything such as a foreign body in her eye. Apply some Terramycin eye ointment from the feed store. She may also need some antibiotics such as Tylan 50 injectable given orally, or oxytetracycline in her water if she has a respiratory disease.