Kathleen Wanstall was born in Rugby on 30 January 1886, the daughter of Richard Cotterill Wanstall and Flora Mary Grant. She was educated at St Margaret's School, Bushey, and trained as a nanny at the Norland Institute in London, 1904-6.

She worked for the Vaux family in Carshalton, 1906, and the Guest family in Poole, 1908-10. She was then employed by the Prince and Princess Wilhelm of Stolberg-Wernigerode of Schloss Schonberg in Hessen, Germany, 1911-19, and travelled with them to the German Embassy in Rome and then Vienna during the First World War. After the War, she worked for the Royal family of Monaco, where she was mainly responsible for the care of Princess Antoinette, the daughter of Princess Charlotte and Prince Pierre de Polignac, who was born in 1920. In 1937, she was awarded the Médaille d'Honneur de Deuxième Classe and, in 1950, she became a Chevalier de l'Ordre de Saint-Charles. She died on 9 May 1967 and is buried in the Cimetiére de Monaco.