This is possibly Mary Louise Kent, the youngest daughter of Charles Kent (1825-1900), a Customs House Officer from 1853 to1882, and his wife Mary Wilson (1837-1937). Mary Louise was born on 4 Dec 1879 and was christened at the Holy Trinity Anglican Church, Launceston, on 29 Jan 1880. On 24 Sep 1902, Mary married Gerald Edgcumbe Senior, the fourth son of Joseph Senior of Watford, England. The marriage took place at the Holy Trinity Church. Mary died in 1957.
Another possibility is that the portrait is of Margaret Louisa Kent, born in Launceston on 5 Oct 1879, a daughter of John Kent and Jane Elizabeth Stewart.