The monarch is central to government in this country in that it is necessary for that person to sign every law, I believe. So let's not talk about smiling and waving and meeting distinguished visitors, any member of the family can do that. Apparently the job is much harder than that, I've been told.
So, that person has to always be reading and signing, reading and signing, reading and signing. You can't pass it on to another family member. If she passes that on, she's either no longer monarch, by definition, or she needs a regent. So she's never going to be able to put her feet up, ever. Unless she loses her marbles. God help her.