Baynton was born in 1857 at Scone, Hunter River district, New South Wales, the daughter of Irish bounty immigrants, John Lawrence and Elizabeth Ewart, although she claimed to be born in 1862 to Penelope Ewart and Captain Robert Kilpatrick, of the Bengal Light Cavalry. This fiction gave her "entrée to polite circles as a governess" and, in 1880, she married Alexander Frater, the son of her employers. They soon moved to the Coonamble district, and had two sons and a daughter. However, Alexander Frater ran off with her niece, Sarah Glover, in 1887, and Barbara moved to Sydney and commenced divorce proceedings. A decree absolute was granted 4 March 1890.