It is likely that this is the bronze described in Diana Cooper's autobiography, The Rainbow Comes and Goes, 1958, p. 220, where for the year 1919 she mentions various wedding gifts including statuettes by Frampton, Mackennal and Reid Dick.

Sir William Reid Dick was a Scottish sculptor known for his innovative stylisation of form in his monument sculptures and simplicity in his portraits. He became an Associate of the Royal Academy in 1921, the year the marble version of this bronze was exhibited in Glasgow, and a Royal Academician in 1928. Dick served as president of the Royal Society of British Sculptors from 1933 to 1938. He was knighted by King George V in 1935. He was Sculptor in Ordinary for Scotland to King George VI from 1938 until his death. As a portraitist his reputation blossomed after his marble mask of Lady Diana Duff Cooper was shown at the Royal Academy in 1922. 

Information: 

This is the bronze version of the marble mask of Lady Diana Duff-Cooper, exhibited at the Royal Academy in 1922 (after the bronze - illustrated in The Graphic, 6 May 1922, p. 18 and The Sphere, 6 May 1922, p. 26), 'a beautiful mask of Lady Diana Duff Cooper, looking modestly downwards' (The Scotsman). Lady Cooper was a friend of Reid Dick, and helped him secure many aristocratic commissions. This bronze belonged to her, and was probably given to her by the sculptor.

Lady Diana Cooper, aristocrat, actress, society hostess, political consort and beauty, was born at Belvoir Castle in 1892. Her supposed father was the eighth Duke of Rutland, but she was in fact the product of a long affair between her mother and the Honourable Henry “Harry” Cust, of the neighbouring Belton estate. Lady Diana first became known as a member of ‘The Coterie’ set in London before the First World War. Following her marriage in 1919 to Alfred Duff Cooper (later Viscount Norwich), who was to serve as a minister in Churchill’s War Cabinet, Lady Diana’s reputation as a society hostess was confirmed. Her reputation as a beauty was cemented with Hoppé’s decision to include her in the 1922 Book of Fair Women. As an actress, her most famous role was as the Madonna in Max Reinhardt’s The Miracle, a role she played on Broadway in 1923 and toured for three years around Europe and in Britain.