In the short story The Soul of the Croupier, Mirabelle is someone that Mr Satterthwaite met during his summer holiday in Monte Carlo. A Parisian stage favourite, she was said to be the present mistress of the King of Bosnia who have showered her with jewels.
Satterthwaite observed that Mirabelle was "amazingly chic". a tall thin woman with wonderful dyed fair hair, a complexion of pale mauve and orange lips. She was dress in "something that looked like a glorified bird of paradise, and she wore chains of jewels hanging down her bare back. A heavy bracelet set with immense diamonds clasped her left ankle."
Her arrival caused a sensation among the casino guests, who wondered how Countess Czarnova, herself a former mistress of the King of Bosnia, would be able to compete.
In the event, the countess appeared in a plain white dress, "a mere staight slip of marocain such as a debutante might have worn" with no jewelry at all. Satterthwaite approved and thought it was clever. "She disdains rivalry and turns the tables on her adversary."