Brenda Anderson was 94 when she died at Flinders Medical Centre on March 16 last year, the same age as her husband Lynton when he died at the same venue on May 1 this year.
Police will allege both died from drug overdoses after being deliberately administered medication.
In Brenda Anderson’s case they will allege the fatal dose came when she was being treated as a patient at the Noarlunga Hospital on March 12, 2022.
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Police will also alleged Lynton Anderson was overdosed at his Hackham home on April 30 this year.
A 62-year-old Craigmore woman, a family member of the Andersons, is expected to be charged with two counts of murder later today.
She will be refused police bail and is likely to appear in court later today or tomorrow, police say.