Lady Forrest (22 October 1844–13 June 1929 Picton, Bunbury), born Margaret Elvire Hamersley, was the wife of Sir John Forrest. Born in Le Havre, France, she was a member of the prominent and wealthy Hamersley family; her father was Edward Hamersley (Senior), and amongst her brothers were Edward Hamersley (Junior) and Samuel Hamersley. She married Forrest in 1876 and enjoyed many years in public life, as John Forrest became the first Premier of Western Australia, and later a federal politician. Their family homestead was called Wilberforce.
Both Margaret River and Elvire River in the Western Australian Kimberley region were named after her.
Lady Forrest had a great interest in fine arts. She was a founding member of the Wilgie Club, which was possibly the first artists' society in Western Australia, and in 1896 became also a founding member of the West Australian Society of Arts. She also had an interest in native plants, and was an accomplished painter of wildflowers. After her death in 1929, her collection was bequeathed to the Art Gallery of Western Australia.
Ellis Rowan visited Western Australia a number of times during her life. In September 1889 she joined Margaret Forrest in a painting tour. At Boolantha Station, north of Carnarvon and Geraldton, they painted desert flowers. Their joint exhibition at the Railway Station Reading Room in Perth on 5 November is thought to have been the first art exhibition ever held in the colony.