In La mystérieuse affaire de Styles, the French adaptation of The Mysterious Affair at Styles, Diane Clément-Roussel is a customer of the Styles beauty center, and the somewhat vague parallel of Mary Cavendish in the original novel. Despite being married to a minister, Diane has an affair with Swan Laurence. The only trait that helps identify Diane Clément-Roussel as Mary Cavendish is that just like the original character she had added a sedative to Èmilie Beauregard's drink.
Her character was portrayed by Alexia Barlier.