As Jade59 asked, what makes you think this? What is she doing?
Generally a blind eye will not react by moving to follow something in its view. Also a blind eye is often "stuck" with a large pupil that doesn't change with changes in light shown. Basically the eye doesn't react to anything. (However blinking and closing the eye still occur as these actions have nothing to do with sight).
I would have your kitty checked by a vet. Other conditions can look like blindness like listed above, but actually is something else and that list is a long one. A vet would have to do an exam to know where to start looking for the cause. If the kitty is running into things on just one side like it "didn't see it"...this could also be a neurological issue rather than blindness. So again, a vet visit is suggested.
Hello and welcome. What makes you think this? Is one pupil larger than the other?