Cathleen Sabine Mann RP ROI (31 December 1896 – 9 September 1959), styled the Marchioness of Queensberry from 1926 to 1946, was a British portrait painter and costume designer for film.

[1][2] Harrington Mann gave Cathleen painting lessons in his London studio, as did the portrait painter Ethel Walker.

Walker continued to tutor Mann even while Cathleen was studying at Slade School of Fine Art in London.

Her work was displayed at the Victoria and Albert Museum, the Musée du Luxembourg, and the Royal Glasgow Institute of the Fine Arts.

[4] The two deaths seemed to have caused Mann to have a nervous breakdown, but it has been said that during this period she produced some of her best work, from landscapes and child portraits to sculpture and abstract paintings.

As Marchioness of Queensberry she used her name and the strength of her personality to break through official difficulties and to commandeer transport by both road and rail to carry numbers of helpless and in some cases crippled people to safety.