Bundle Brent was the eldest daughter of Clement Edward Alistair Blunt, 9th Marquess of Caterham. She had two sisters, Daisy and Dulcie. She described her late mother as having “got tired of having nothing but girls and died". Her mother "thought someone else could take on the job of providing an heir”. Bundle’s uncle, the 8th Marquess, was Foreign Secretary in the British Government (a circumstance possibly suggested by Marquess Curzon of Kedleston's having held that post from 1919-1924).
Bundle’s age is not given in either novel, but it seems a reasonable conclusion that the years 1925-1929 cover roughly her early to mid twenties. That would be consistent with ages given or hazarded for characters whom readers would assume were, broadly speaking, her contemporaries. As a child she was "long-legged" and "impish", growing into a “tall, dark” adult with an “attractive boyish face”. She was resourceful, headstrong, vivacious and charming, with sharp, penetrative grey eyes that could be disconcerting to others.
"Simply it" Bundle was very much a young woman of her times, with many of the characteristics of a "flapper". Her future fiancé, drawing on terminology made popular by the film, It (1927), starring Clara Bow, remarked to a Foreign Office colleague, "Don't you know Bundle? Where have you been vegetating? She's simply it".
When Bundle's father, with whom she clearly had a strong bond, observed that “you modern young people seem to have such unpleasant ideas about love-making", she attributed this to her having read The Sheik ("Desert love. Throw her about, etc."), the novel by Edith Maude Hull (1919) on which Rudolph Valentino's celebrated film of 1921 was based.
Bundle owned a Hispano-Suiza car, possibly an H6B, first marketed in 1922, though the model is not in fact identified. On her own admission, she tended to drive too fast and some, including Lord Caterham, were “terrified” of her driving. On one occasion, she thought that she had run a man down, whereas in fact he had already been shot dead. Bundle’s clothes were of the corsetless kind that young women favoured after the First World War; she wore only a “negligible trifle” under her dress. Although her attitude to politics and politicians was somewhat ambiguous, she claimed to be a socialist and indeed was described by a future suitor as "a red hot socialist if she’s anything at all".