The Queen is the Head of State. There are responsibilities that come with being Head of State. If a person is so old, or infirm, that they can no longer get out of a car or sit in a church, it is my personal opinion that they are not fulfilling the role of head of state. Irrespective of how long they have lived, or the service they have already given, a person should be self aware enough to realise that they are no longer capable of giving the service to the nation that they always have, and that perhaps its time to pass those responsibilities on to a person who is better able to perform them.
But with a hereditary monarchy with a strong objection to abdication, you get what you're given.
Monarchists want this woman to have the title and role of Head of State until she dies (sorry, distasteful).
I'd rather we had somebody as Head of State who is able to perform the duties that role encompasses. I do not feel that I am the one who is being disrespectful to a person who has devoted their life to fulfilling a role that we expect of her, its the people who think she's got to stay there till she dies that are asking too much of her.