I would add that your mother should also sit in an aisle seat, to make standing up to make use of lavatory much easier, as well as simply being able to walk about should the desire arise. Although my grandmother no longer flies (she's nearing 90), her last few years of flying were always mandatory in business class. For decades she liked the window seat to stare outside, but after a particularly distressing flight in the new Club World (now old) by the window when it was rather difficult to get to the aisle, we never made that mistake again. After that it was always an aisle seat, and she very much preferred that (and the window seat passenger did too, as she never put the seat in bed mode).