Sue, no perches on nest boxes – this makes it too easy for predators or other bird species. If the female is getting around well enough to take care of her nest, then I wouldn’t do anything at this point. If she weren’t already nesting I might suggest calling a rehabber, but this could just be an old injury or even a congenital defect.
On the distant box nesting, I’d leave it be for now. You can be watchful, but unless you can watch every second, you can’t be certain that the nest has been abandoned. Do you know when the last egg was laid? Can you feel the eggs to see if they are warm? Can you place a piece of grass across the nestbox opening in such a way that the bird will have to dislodge it if they go into the box?