My goodness! - if she doesn't want to be wheeled around, or drive herself, in a wheelchair she's not being a good Christian; or she should consider others who are confined to them and, presumably, raise 'awareness'; she's, apparently, "daft"; she should give up and hand over to Charles... she looks so frail - how long will she last, etc, etc, etc.
As a Republican, I think she should do what makes her feel most comfortable, mentally and physically, in her role as Queen and as a human being. If she can't perform all her previous duties, she'll elect someone to replace her for whatever occasion, she'll continue to peruse and sign the necessary documents, she can be consulted sitting down - with others also seated, if necessary. Basically, she can be accommodated!
After a lifetime doing what she considers to be her duty, with herself and her family living life like fish in a tank, and is still well-respected... I think she's earned the right, ultimately, to decide for herself whether she's seen in a wheelchair or not. Either way, there's going to be endless speculation about the state of her health, or about her frailty. The woman is going to be criticised if she does use a wheelchair ("she should hand over the reins / reign to Charles") and equally damned if she doesn't use a wheelchair ("she's so frail, she should accept the inevitable").
Whatever she decides, she'll give it careful thought and look at the situation from all angles. Let Brenda decide for Brenda. You will not see her like again, she's the end of an era. Let her do it her way...