A vision impairment does not need to “prevent, or significantly or severely restrict,” an individual’s ability to see in order to be a disability, as long as the individual’s vision is substantially limited when compared to the vision of most people in the general population.
And it sounds like her employer is doing the right thing. But if ever she feels she is not being treated fairly, she should talk to a lawyer to be sure. Don’t just let it slide because she has one good eye. Hell it might be good to talk to a lawyer anyway, so she knows what to look out for in the future if things happen to change.