I kindof hope the Mary Kline Still Life appears in the next film.
Similar to the Archibald Leland Sutter Still Life, it is possible that the Mary Kline Still Life is completely immobile and confined to its chair.
Seems unlikely to me. Given that the Archibald Still Life is in a wheelchair, it's pretty certain that the Frontrooms human (who presumably exists or once existed) that the Archibald Still Life is (imperfectly) copied from also exclusively uses a wheelchair. That's probably why the Archibald Still Life never walks.
Mind you, the Bearded Still Life doesn't ever stand or walk or move, but the Redheaded Still Life stood very still except in a few specific circumstances. My guess is that the Bearded Still Life and/or the Mary Kline Still Life may well be capable of movement and may well demonstrate that in sequels.