Following the war, Hathaway continued to promote Sark's tourist trade and advocated building a new harbour. In 1949, she and her husband welcomed
Princess Elizabeth, Duchess of Edinburgh (later Queen Elizabeth II) and the
Duke of Edinburgh, who opened the new harbour. The same year, Hathaway became
Officer of the Order of the British Empire. Sibyl and Robert Hathaway's happy marriage ended with his death in 1954, to Sark's first seigneur,
Hellier de Carteret, Hathaway was made
Dame Commander of the Order of the British Empire at
Buckingham Palace. She then jokingly referred to herself as a "double dame". However, soon after her quatercentenary, her daughter, Douce Briscoe, died in 1967, having struggled with alcoholism for a long time. In 1969, Hathaway became increasingly worried by the
Royal Commission on the Constitution's intrusion into her affairs. At the same time, she had a sharp dispute with the Chief Pleas, claiming that its members violated the laws they themselves had passed and that their misconduct threatened to make her tourism campaign futile. She shocked the islanders by announcing her intention to resign the charter of the island back to the Crown "in somewhat the same way as the
Hereditary le Mesurier Family did in Alderney" and to recommend that the government be taken over by Guernsey. The threat was effective; regulations were suddenly enforced much more strictly. By the beginning of the next year, Hathaway retracted her announcement, having been persuaded "by an enormous number of letters and requests". ==Death==