She was born at Dysart House in Fife, the eldest daughter of the Scottish Conservative politician Robert St Clair-Erskine, 4th Earl of Rosslyn.

Charles Maynard, making them half-sisters to Daisy Greville, Countess of Warwick and Blanche, Lady Algernon Gordon-Lennox (mother to Ivy Cavendish-Bentinck, Duchess of Portland).

She married Cromartie Sutherland-Leveson-Gower, Marquess of Stafford, eldest son and heir of the 3rd Duke of Sutherland, on 20 October 1884, her 17th birthday.

Her caricature appears in Arnold Bennett's Clayhanger Family novels as a countess with an ‘interfering meddlesomeness which so frequently exasperates the Five Towns’.

[7] After the outbreak of the First World War in 1914, she organised an ambulance unit that saw active service in the siege of Namur, Belgium.

[1] It was part of the estate of press agent Benjamin Sonnenberg, and was sold at auction by Sotheby's in 1979 for $210,000, setting a record for the artist's work.

A set of ten oil paintings by Victor Tardieu (1870–1937) record the tented field hospital established and run by Millicent at Bourbourg, 12 miles (19 km) south-west of Dunkirk, during the summer of 1915.The dedication on No.2 reads: "à Madame la Duchess M de Sutherland/Hommage respecteux et tres reconnaisant/d'un simple soldat".

The series went on sale at Abbott and Holder gallery in London in early 2012,[11] and was acquired by the Florence Nightingale Museum.

[12] She wrote novels, including One Hour and the Next (1899) and a collection of short stories, The Winds of the World (1902), and a play in blank verse.