 She was the youngest daughter of John Anderson, who served as the second mayor of Christchurch, and her brother, also called John Anderson, played rugby for Scotland against England in 1872, and was the first New Zealander to appear in a rugby international.One of Millton's brothers, Edward, also represented New Zealand in rugby union.A batsman, Millton was captain of both the United Cricket Club in Christchurch and the Canterbury provincial side.