This almost sounds like some sort of seasonal allergy, except that it's weird to only affect one eye. When you said you think she can't see out of that eye, are you saying she can't see due to this issue or you think she's actually blind in that eye? If you think she's blind in that eye maybe she banged/bumped/poked it on something (grasping at straws here) and it got irritated/injured. I don't really buy that myself though since they have all those whiskers and sensory hairs to warn them when they're close to something.