Elmhirst was also a first cousin of Lady Alice Montagu Douglas Scott, who became the Duchess of Gloucester after her wedding to Prince Henry, and an aunt-by-marriage of Queen Elizabeth II.
The Countess Spencer, Cynthia, paternal grandmother of Lady Diana, Princess of Wales, was her 2nd cousin.
On 1 November 1927, at the age of 19, Marian married Colonel Andrew Ferguson (10 October 1899 – 4 August 1966), in London, England.
In 2019, Marian's granddaughter Sarah, Duchess of York, revealed in a speech that her uncle had died as a result of an allergic reaction after he ate a crab sandwich.
Ronald Ferguson died on 16 March 2003 from a heart attack, after a lengthy battle with skin and prostate cancers.