WE HAVE THE SAME PROBLEM RIGHT now and are treating it with tetracyclin in their drinking water. i bought some black copper marans at a chicken swap and they must have infected some of my flock. my ameraucana hen was much better after 3 days but the maran pullet died. my question is are the eggs safe to eat?
Sounds like maybe she did injure her eye. Especially since the rest are doing fine, and no respiratory symptoms.
I'd hold off treating them all since they aren't showing any symptoms.
If this one is isolated, then treat her with the antibiotics just to see if maybe the injury has gotten infected or who knows why it's swollen and the eye shut. I think it's good that you aren't seeing any discharges though.
Have you tried the terramycin yet? My silkie started in with a swollen eye last week and I immediately attacked it with the terramycin. The swelling was gone within 3 days. The terramycin is applied directly to the eye.