It is likely that she has been declining for years. Since long before COVID or vaccines. AD takes years to develop. It is exceptionally rare to have it go from zero to dead in 18 months.
She’d been somewhat active, publicly, up until recently. Even her own publicists confirmed this was a ‘brief’ illness.
But, you cover for what you must.
My in-laws know of two people, from their church, who were diagnosed, and, sadly, succumbed to alzheimer’s, very quick, recently.