I think people would rather see her in a wheelchair than not at all. It would also save her from needing to struggle to stand then sit then stand and could provide a dignified way of coping for longer with public duties, and yes! an inspiration to other wheelchair users and an encouragement to any hesitating to use one.
Without one I think she will rarely be seen in public after the Jubilee. If mobility is the only real issue that will be a shame.
Do you get a mot at the doctors?
I need advice for a mutually messy situation

pushing the chair, in full uniform. My poor husband, decades younger than QE and formerly a very, very fit man, has to make do with me. It was a hard adjustment, but I admire him for making it.