She briefly attended Tunbridge Wells School of Art in 1939, before enlisting in the Auxiliary Territorial Service during World War II.

[2] She worked as an art teacher, painter, and textile designer before becoming a full-time book illustrator.

[4] Fortnum's best-known works are her illustrations of Michael Bond's character Paddington Bear.

[7] Although her pen-and-ink drawings of Paddington were done in black and white, some of them have been coloured by other artists, including her step-granddaughter Caroline Nuttall-Smith.

[6] One of her Paddington illustrations was used by the Royal Mail in 2006 for one in a series of first class stamps that celebrated animals from children's literature.