Beatrice "Bumble" Dawson, the prolific and versatile British costume designer, began her career in the theatre with a production of The Duchess of Malfi at the Haymarket Theatre in 1945. She started her film work with the 1948 postwar drama Night Beat for British Lion Film Corporation. Dawson continued working for both film and the stage throughout her career. With Trottie True (1949), the lavish costume musical about a Gaiety Girl who graduates from the stage to marriage with a peer, Dawson herself found the success that elevated her to the top rank of Britain's designers. Actress Jean Kent, a lovely redhead, was the first of the screen beauties to be showcased by Dawson's elegant costumes—the film itself is chiefly noted for its brilliant use of Technicolor.
http://www.filmreference.com/Writers-and-Production-Artists-Ch-De/Dawson-Beatrice.html#ixzz6cP2CWqFC This would put her at 38 when she first started theatrical designing, she must have done something before then.
I can’t find her on thepeerage.com.