VanKoughnet married Hugh John MacDonald, who was ten years her senior, on April 26, 1883, at St. Stephen's church in Toronto.
[4] Later, when Hugh John was made a Knight Bachelor in 1913, she officially became Lady Agnes Gertrude Macdonald.
When the Duke and Duchess of Cornwall visited in 1901, she attended a luncheon in their honour and was seated at the head table.
She also attended a luncheon at the Government House of Manitoba in 1939 celebrating a visit from King George VI and Queen Elizabeth.
[10] While serving as minister of the interior and superintendent general of Indian Affairs, Macdonald often left notes in the margins of his political papers with instructions for VanKoughnet.