Lizzie Ida Grace Willis was born in Wellington on 29 December 1881, one of 13 children of Alexander James Willis, secretary to cabinet and clerk of the Executive Council, and his wife, Amelia Annie Nicholson. The family lived in Thorndon and then moved to a spacious house at Johnsonville with five acres of lawns, gardens, fields and a tennis court. Ida, as she was known, received her education at Johnsonville School, Fitzherbert Terrace School and Wellington Girls' High School. She trained as a nurse at Wellington District Hospital from 1907 to 1910. Following her registration at the age of 28, she joined the staff at Wellington Hospital as a ward sister, then as night sister earning £70 a year.
After her father died in 1910 she went to Australia with her mother and sister. She trained as a midwife at the Women's Hospital, Melbourne, found work at Bulli Cottage Hospital, south of Sydney, and obtained a certificate from the Royal Sanitary Institute, London. By 1912 she had returned to Wellington, where she worked at a private hospital with Louise Brandon, a fellow Wellington Hospital trainee.
In August 1914, while Willis was on holiday in Fiji, the First World War started, leaving her stranded. She joined the advance party of the New Zealand Expeditionary Force, which called in that month on its way to German Samoa. Six nurses had been seconded for work at Apia Hospital, and she accompanied them, becoming a member of the force. Once New Zealand had taken military control the seven New Zealand women replaced the German nurses.
Following her 10-month assignment there, Willis returned to New Zealand and took charge of a ward of soldiers suffering from cerebrospinal meningitis at Wellington Hospital. In July 1915 she became one of a contingent of 69 New Zealand Army Nursing Service (NZANS) members on board the Maheno bound for Egypt. Willis worked at the New Zealand General Hospital, near Cairo, which had beds for only 250 patients, but had to accommodate 650. Large numbers of soldiers from Gallipoli, many emaciated from dysentery and poor food, were admitted between August and November 1915.
In June 1916 Willis transferred from Egypt to England with No 1 New Zealand General Hospital, at Brockenhurst, before being moved to No 1 New Zealand Stationary Hospital at Amiens, France, 15 miles from the front line. Conditions were extremely difficult: hospital staff, nurses, orderlies and doctors worked continuously for up to 36 hours at the three tables in the huge operating theatre, stopping only to plunge their gloved hands under running water and disinfectant. She also went to Bruay-en-Artois to a British unit during the battle of Vimy ridge. In one morning a thousand stretcher cases were admitted to the hospital. On occasions she acted as sister in charge of an advanced dressing station.
After nearly a year at Amiens, the New Zealand Hospital moved to Hazebrouck. Here, during raids, a tin hat became part of the nursing uniform. When Hazebrouck township was shelled, Willis, along with a thousand patients and staff of No 1 Stationary Hospital, was evacuated to a British hospital. The New Zealand Stationary Hospital subsequently reopened at Wisques, 12 miles from Hazebrouck. Here the staff suffered a bitterly cold winter, with hard frost. Duckboards placed on walkways between tents helped to avoid the mud, but a number of nurses suffered from trench foot. Their feet needed to be soaked daily in hot water and rubbed with whale oil; some nurses were issued with men's socks and gumboots to accommodate their swollen feet. For her war work Willis was made an associate of the Royal Red Cross in 1917, and was twice mentioned in dispatches.
After the war Willis returned to New Zealand and was employed at Featherston Military Camp, where the influenza epidemic cost the lives of one sister and 75 officers and men patients, while hundreds of men were stricken down. Several cerebrospinal meningitis cases followed. In January 1919 she was appointed assistant to the matron in chief of the NZANS, Hester Maclean, whom she assisted during its demobilisation.
By February 1920 Willis had moved into administrative work as assistant inspector of public hospitals, a position she would hold for the next 20 years. During this period she continued to be a member of the NZANS reserve, attending regular camps and giving instructions to orderlies of the New Zealand Medical Corps. In 1929 she was recalled from the reserve and appointed a matron of the NZANS. In 1932 she was appointed principal nurse, and in 1933 matron in chief. As such, during the outbreak of the Second World War, Willis directed overall nursing proceedings. Approximately 650 trained nurses took their place at military hospitals, on board transport vessels and at military camps in New Zealand and overseas, and Willis co-ordinated their war services. In 1944 she was appointed an OBE in recognition of her nursing and military service.
Willis retired from the army and nursing in February 1946. For the next 22 years she lived with her sister at Raumati Beach, enjoying overseas trips and the company of family members. She never married and died at her home on 7 March 1968.