Obviously I’ve no insight whatsoever on her state of health, but it is also perfectly possible she has become wheelchair bound due to her advancing age and still be perfectly lucid, mentally competent and have a number of years in her, as countless millions of people go through around the world all the time.
It goes without saying that in an ideal world being wheelchair bound but otherwise reasonably healthy, comfortable and willing should never be an impediment to carry on with your life, even if you’re the bloody head of state. In fact it would be a wonderful advertisement for further acceptance in everyday life of disabled people if she were to show up and open Parliament tomorrow on a wheelchair. But I get the feeling either Brenda herself or whoever is in charge of ‘The Firm’ might think it undignified or something to be embarrassed about.
Then again she might be unwell enough to at least prevent her from attending the event. But I certainly wouldn’t put it past that lot to consider the sight of Her Maj being wheeled in to an official duty unacceptable.