She later focused her research on the Ancien Régime (the Kingdom of France from the Middle Ages to the French Revolution).
[2] She "achieved an international reputation" with The Ancien Régime,[4] with reviews describing it as "remarkable and absorbing"[5] and "a lively, thought-provoking essay in historical revision".
[2] Her mother Vivien Behrens (1880–1961), the daughter of Sir Cecil Coward, was reared as a Christian.
[4] Her research in the mid-1930s was focused on Henry VIII, and she published academic papers on this period including on his divorce and on resident diplomats.
[10] She retired from full-time academia in 1972, but continued to be an active academic as a fellow emerita of Clare Hall from 1972 to 1986.
[10] Her final book, Society, government and the Enlightenment: the experiences of eighteenth-century France and Prussia, was published in 1985; she was eighty-one.