Adeline de Smidt was born in South Africa in 1882, the daughter of Abraham de Smidt and Gertrude de Smidt (née Overbeek). The de Smidt family (originally from Antwerp and Middelburg) owned the estates of Groote Schuur (Great Barn) and Westbrook under Table Mountain.

The de Smidt family moved to England in 1890, settling at 1, Belgrave Place, Brighton then at 18, Chesham Place, Brighton (a house which is almost opposite the former Hankey family home at number 1). Adeline was educated at Brighton High School and then at Brighton Art School where she studied to become an art teacher.

Adeline met Maurice Hankey at Christmas in 1902 and they were married on 16 September the following year. They had a very strong and supportive relationship. On 4 July 1905, their first child Robert (Robin) was born. In 1907 the family moved to Malta, returning the following year to settle at the Corner House, Oxted, Surrey. On 5 February 1909 Ursula was born, then on 27 April 1911 Christopher. The family moved to Highstead, near Limpsfield, Surrey and on 1 September 1914 Henry was born. In 1916 a fifth child was still born.

Adeline supported her husband's career and accompanied Maurice to social engagements with prominent politicians and public figures. She also accompanied him to several of the peace conferences (to which he was Secretary) during and after the First World War, including the 1919 Paris Peace Conference and the 1922 Genoa Conference. Adeline was seriously ill in 1918 and did not fully regain her strength until 1931, when she was advised to follow a "Nature Cure" diet which restored her health. In 1934, Adeline and Maurice went on a "World Tour", visiting Australia, New Zealand and Canada so Maurice could inspect the empire's defences. In the late 1940's and 1950's they made several trips to Egypt as Maurice was a Director of the Suez Canal Company. Adeline nursed Maurice during his final illness until his death in 1963. She continued living at the family home at Highstead and died in 1979.