Garnsey was the daughter of Tasmanian politician B. S. Bird. The family moved from Hobart to Flight's Bay in the 1880s, then to an orchard property on Bruny Island in 1892. After the death of her father years later Garnsey and her sister ran the property. These experiences are described in Romance of the Huon.
In 1893 Garnsey and her sister left for the mainland. Garnsey trained as a nursing sister in Rockhampton. She lived in Western Australia until the death of her first husband, then returned east to work as Matron at the New England Girls' Grammar School. She married the Rev. Canon A. H. Garnsey, Warden of St. Paul's College, University of Sydney in 1922.
