She was born on 29th June 1907, the daughter of Colonel George Stratford Mardall, OBE and Helen Jura Campbell McEwen and was educated at the Michaelis School of Art at the University of Cape Town where she shared the Michaelis Prize in 1928. She studied under the London portrait painter Percival Small and held exhibitions in Cape Town in 1938 and 1963, had a permanent exhibition at the Mount Nelson Hotel and also exhibited in London. She was a figurative portrait painter and flower painter who worked in oils, pastels and watercolours. She served at the Admiralty, Whitehall as a war artist during the Second World War. She married Robert Fitzwilliams on 19th August 1948 in Cape Town and died on 24th September 1965 in Cape Town.

• Cape Argus, Cape Times 19/21 April 1928 ( profile and photographs of Natalie Fitzwilliams, Michaelis Prize, University of Cape Town)
• Photograph and review and diary piece ( her exhibition, Ashbeys Galleries, Cape Town, 1938)
• The Tatler's Register of Engagements 18 August 1948 (photograph)
• Cape Argus and Cape Times wedding photographs and articles 20/21/28 August 1948. The Tatler's Review of Weddings 6 October 1948 (wedding photograph)
• Cape Argus 14 August 1962 (profile of Natalie Fitzwilliams, reproduction of "Roses" hung at Royal Institute of Oil Painters, London)
• Die Burger 5 September 1962 (review and reproduction of "Roses")
• Cape Times 28 February 1963 (review "Artist Shows Her Love for Flowers" of her exhibition)
• Cape Argus February 1963 (her photograph and reviews of exhibition)
• Daily Representative Queenstown 24 May 1963 ("Arum Lilies")
• Cape Argus 18 September 1964 ("Roses" hung at Royal Institute of Oil Painters, London)
• Daily Representative, Queenstown 22 June 1965 (her self-portrait)
• Cape Argus 18 August 1965 ("Roses" hung at Royal Institute of Oil Painters, London)
• Obituaries SABC News 24 September 1965 Cape Argus and Cape Times 25 September 1965, Daily Representative, Queenstown, May 1966.