Simpson Manor was purchased in 1861 by the Sisters of Saint Anne. When the first wing was added for the boarding school, in 1864, the Sisters of Saint Anne officially made the Manor their headquarters.

As Father Piché wrote:
The opening of the boarding school in Governor Simpson’s house took place in Sept. 1861. As the premises were not large enough, the Sisters built their boarding school between 1862 and 1864. … A further, 90-foot addition was made in 1888. The House of the Governor of Hudson’s Bay [Company] was demolished in 1888. It was replaced by the current Chapel, which measures 150 feet by 60.