If other members of the family are fulfilling the role of HoS, why is she still there? There's no shame in being Queen Mother, is there? or Dowager Queen? I think its because she has been Number 1 for 70-odd years and can't imagine someone else being in that position. I can understand that, actually.
Totally agree, Alegrias1
However, senior members of the Royals have performed umpteen engagements without her being there with no ado.
This is a list of the engagements of 2019
Princess Anne: 195
Prince Charles: 177
The Queen: 174
Prince Andrew: 139
Prince Edward: 119
Prince William: 108
Prince Edward, Duke of Kent: 05
Prince Richard, Duke of Gloucester: 105
Prince Harry: 98
Camilla, Duchess of Cornwall: 81
Sophie, Countess of Wessex: 81
Kate, Duchess of Cambridge: 56
Princess Alexandra: 43
Birgitte, Duchess of Gloucester: 42
I'm sure the Queen will still be doing certain engagements but it's not as if she has ever done them all herself.