McEwan reports sprawling under a wattle tree and scribbling away as a child growing up in the Blue Mountains. She entered stories, poetry and paintings into competitions in the Sydney Sun's Sunbeams supplement and The Australian Woman's Mirror 'Piccaninnies' Page' in the forties. She played the piano, rode horses and learned fencing.

From 1946, she was actively writing short stories for publication and working on children's books. She secured a journalism cadetship at the Lithgow Mercury, and had short stories in that paper (21 May 1947) and the Sydney Morning Herald's 'Playtime' supplement (24 September 1947). In December 1947 she moved to the Lachlander and Condobolin and Western Districts Recorder.

From October 1949, McEwan joined the literary staff of K. G. Murray Publications in Sydney. Editor-in-Chief Frank Greenop recognised here potential and she soon became assistant editor of House and Garden Magazine, and then editor for True Romance, True Stories and Digest of Digests. Her role included selecting the US stories to be reprinted and editing them to be less American.

During this tenure on Murray's True Romance Magazine group, McEwan wrote a comic story for Romantic Adventures #3, with art by Peter James.

From the late forties and during the fifties, McEwan also wrote some short stories wrote for the Australian Woman's Mirror.

An artist colleague at K.G. Murray, Herbert Young, secured commitment from the Sydney Morning Herald for a schoolboy adventure strip. He proposed a collaboration and the result was 'Danny Martin', running 21 half-page colour weekly strips in the Sunday Herald from 1 April 1951. The story focused on a group of schoolboys who thwart an attempt by German spies to take over Cliff College, a private boarding school near Sydney.

From mid-1951, McEwan spent just over two years working overseas. She wrote international news services, toured Italy by bike and hitch-hiking, participated in fencing championships, worked as a stunt double for sword-fighting (Daughter of the Black Pirate) and horse-riding scenes (The Crossed Blades) in films, and wrote television scripts in Los Angeles (such as Makers of Music the Bach Vivaldi Story). On her return to Australia, she did a number of radio talks based on her travels.

Building on her international television experience, in mid-1954, McEwan took up a position at the fledgling television studio at Pagewood Sydney, working on scripts for The Adventures of Long John Silver series. The series was made in colour in Australia for international markets before the development of television in Australia. She wrote documentaries for the film division of the Australian News and Information Division (later Film Australia). In 1960, she won a Commonwealth television play competition exclusively for women.

From 1964 to 1967, McEwan wrote around 20 pulp novels for Horwitz Publications, beginning with the commerce section of an encyclopaedia of Australia and New Zealand. For a period her output nearly rivalled Alan Yates (Carter Brown), which led to burnout and writer's block. She studied law and changed career, working as a barrister from 1989 to 2010. She wrote two further books, Great Australian Explorers (1987) and The Survival Factor (1989) with Rowley Richards.

In 1990, McEwan shared a credit with her daughter Vashti Osterberg-Olsen on Art on the Cove: a Collection of Australian Art.