Fanny Wilson was born on 25 May 1874 at Christchurch, New Zealand, the daughter of Mary Jane Whitto and her husband, Samuel Wilson, a labourer. Fanny's father had served in the Crimean War and told her he owed his life to Florence Nightingale. Bedtime stories of 'The Lady with the Lamp' inspired Fanny to be a nurse when she grew up. By 1895 both her parents had died, and she and a sister kept a small home together by doing needlework. When their young brother had finished his apprenticeship, Fanny was able to begin training for the profession she was determined to follow.
During these years, spent at Wellington District Hospital, Wilson's pay barely covered the cost of her shoes, stockings and study books. She sat her final examinations in December 1908 and was registered as a nurse in January 1909. She continued nursing at the hospital until 6 August 1914, when she obtained leave of absence from her duties as a theatre sister to join the first contingent of nurses going to German Samoa with the New Zealand Expeditionary Force. She was attested for service on 11 August and was described at the time as 5 feet 6 inches tall, 10 stone 10 pounds in weight, with brown–grey hair and brown eyes. Fanny Wilson sailed on the Moeraki with No 4 New Zealand Field Ambulance on 15 August. During the voyage to Samoa the nurses inoculated all the servicemen on board. In Samoa they were part of the New Zealand Medical Corps working at the general hospital in Apia.
The establishment of the New Zealand Army Nursing Service was authorised by cabinet in January 1915, and Fanny Wilson returned to New Zealand in March in time to be among the first 50 members of the nursing service to be sent to England. The nurses left on 8 April on board the Rotorua. Two weeks after reaching Plymouth they embarked for Egypt, arriving at Alexandria on 16 June. Wilson worked as a theatre sister at No 2 New Zealand Stationary Hospital near Cairo (renamed No 1 New Zealand General Hospital in 1916). For her service there she was mentioned in dispatches in March 1916.
The hospital moved to Brockenhurst, England, in June 1916. As sub-matron Wilson was put in charge of the section in the converted Balmer Lawn Hotel. Two months later, as acting matron, she was transferred to the New Zealand Convalescent Hospital at Hornchurch, and on 28 August she was promoted to matron.
In January 1917 Fanny Wilson became matron at No 2 New Zealand General Hospital, Walton-on-Thames, one of New Zealand's largest hospitals in England. She was awarded the Royal Red Cross, second class, for valuable services in 1917, and mentioned again in dispatches in 1918. She received the Royal Red Cross, first class, in April 1919. Wilson spent her embarkation leave visiting France. After returning to New Zealand she was discharged from the New Zealand Expeditionary Force in February 1920, and placed on the active list of the Territorial Force. In September that year she was placed on the Reserve List.
Together with Vida MacLean, Fanny Wilson then ran a private hospital in Wellington. She left after three years to train as a midwife at St Helens Hospital, Wanganui. From 1925 to 1929 she worked in the antenatal clinic at St Helens Hospital, Christchurch, and from 1930 until her retirement in 1937 she was matron of The Limes Private Hospital, Christchurch. On the point of retiring, she represented New Zealand nurses at the International Council of Nurses conference in London. While in England she visited the home of Florence Nightingale. Wilson had meanwhile continued her involvement with military nursing. In November 1923 she became deputy matron in chief of the New Zealand Army Nursing Service and from May 1931 to July 1933 she was matron in chief.
Fanny Wilson was visiting Singapore when the Second World War broke out. She returned home and served the Canterbury centre of the New Zealand Red Cross Society for the duration of the war. Around the age of 80 she did some broadcasting in Christchurch during a recruiting drive for trainee nurses. She died in Christchurch, on 11 September 1958, having never married. She was remembered for her tact, her ability to combine human warmth with efficiency, and for being a brilliant and witty conversationalist.