Chickens can suffer blindness from injuries, infections, from vitamin deficiency, from diseases, such as ocular Mareks disease and AE (avian encephalomyelitis,) and from cataracts. Have you ever had Mareks or an unusual death in any of your chickens? It would be hard to know for sure what the cause was, but both AE and Mareks can cause the grey eye. Hopefully, it is just another cause. She should be able to get along okay as long as she can find food and water. My Polish hen who was blind in an eye would occasionally go outside the gate and we had to sometimes go and find her.