But she is 90. 90!!!
You can see the stoop in her walk, she is slowing up physically. Having "away days", "walkabouts", a weekly meeting with the PM (which happens even when she is on "holiday" in Balmoral, and having to oversee dinners and events, and make small talk with hundreds of people...
Yes she has cleaners and cooks and aides, but there is still a lot that she has to oversee. It must be incredibly draining.