I read something interesting on the thread attached on here. It suggested that Charles could well be 80 when he acceeds (is that the right word?) the throne. William, in turn, could also be of a fairly advanced age.
So, in remaining on the throne, Queenie could actually be setting a precedent for very old monarchs. Not sure that's a good thing for the country.
I reckon Queenie's doing it on purpose. Maybe she thinks that abdicating will cause a constitutional crisis, and pertinent questions will be asked about the relevancy of the Family.