Cowan was born on Glengarry station near Geraldton, Western Australia. She was the granddaughter of two of the colony's early settlers, Thomas Brown and John Wittenoom. Cowan's mother died when she was seven, and she was subsequently sent to boarding school in Perth. At the age of 15, her father, Kenneth Brown, was executed for the murder of her stepmother, making her an orphan. She subsequently lived with her grandmother in Guildford, Western Australia until her marriage at the age of 18. She and her husband would have five children together, splitting their time between homes in West Perth and Cottesloe.