In 1940, Duke became a lecturer at the University of Reading.[1] During WWII, she contributed to the war effort via her work with the Girl Guides.[1] She was posted to Greece with the Guide International Service between 1944 and 1946.[1] During this time, she worked at Greek refugee camps in Egypt, ensured that relief supplies reached a women's prison in Athens, and accepted the arms surrendered by ELAS guerrillas in Amphissa.[2] After the war she was instrumental in rebuilding the Guide movement in both Germany and Greece, and in Britain she served on the national education panel at Girl Guides' headquarters.[7]
In 1946, Duke returned to her alma mater, Girton College, Cambridge, where she had been appointed an assistant tutor.[1] She would remain at Girton until she retired.[1] In 1951, she was promoted to tutor and succeeded Norah Christina Jolliffe as director of studies in classics.[2][8] She officially became the college's first senior tutor in 1968, holding the post until 1974.[9] She additionally taught palaeography within the Faculty of Classics, University of Cambridge, where she was an assistant lecturer from 1952 and then a lecturer from 1957.[9] In 1982, she retired from full-time academia and was made a life fellow by Girton.[1][9]