[4] Gwen's father John Lusby was a school principal and classics master in country NSW, and so the family moved around the state until his eventual teaching appointment in Sydney.

[10] In May 1942, The Daily Telegraph reported that "for the first time in the history of Australia, women doctors have been enlisted in the AIF", and that Gwen was one of six serving at Concord.

Elder brother Jack Lusby, a well known cartoonist and short story writer, fought with the RAAF in the Mediterranean Theatre; and brother Maurice Lusby, was sent to Washington and London as Australian Scientific Research Liaison Officer[14] (a radio physicist, he worked with Robert J. Oppenheimer, the atomic bomb scientist).

While her husband studied for his Fellowship of the Royal College of Surgeons, Gwen became the breadwinner, working as a thoracic physician at Brentwood Hospital in Essex.

Gwen's career was largely interrupted by caring for their six children - Margaret, Paul, Justin, Judith, James and Peter - but in 1973 she nonetheless appointed Fellow of the Royal Australasian College of Physicians.

After Fleming's death, Marie Bashir, then Governor of New South Wales, described her as "an outstanding Australian woman who was an inspiration to so many who had the privilege of meeting her – both within the medical profession and beyond".