Mary Anne Reidy was born on 17 June 1880 in the Kilmihil district of County Clare, Ireland, the fifth of ten children of Mary Sharkey and her husband, John Reidy, a farmer. She grew up in a Catholic family, living with her nine brothers on a 73-acre dairy farm and attending the local elementary school. Her parents had met and married on the West Coast of New Zealand, and in 1896, after the death of her mother, her father sold the lease of his farm and returned to New Zealand, hoping to buy land.
By 1902 the family was living in Auckland. Mary kept house for her father until she started domestic work at Mater Misericordiae Hospital in 1904. She was soon nursing with dedication, but often without wages as the Sisters of Mercy were struggling to make ends meet. In 1911 she moved to Waikato Hospital for formal nursing training, which she completed in 1914.
Encouraged by her father, she enlisted in the New Zealand Army Nursing Service on 17 January 1916 and sailed for England the following week. There Reidy cared for casualties from the front in the military hospital at Colchester and in October transferred to No 1 New Zealand General Hospital at Brockenhurst. In October 1917 she moved to No 1 New Zealand Stationary Hospital at Wisques in France. Colleagues nicknamed her 'Ten Franc Reidy' for her habit of borrowing 10 francs to lend to soldiers for a drink or tobacco. Many stories are told of her persistence in seeking justice for the men and they in turn regarded her as the 'most beloved and respected Sister in the hospital'. When the hospital closed in December 1918, Reidy took leave in England before sailing on the Corinthic for New Zealand in March 1919. The traumatic effects of war nursing, and the camaraderie with the diggers, remained with her for the rest of her life.
On returning to Waikato Hospital she was assigned to the training school. However, she did not enjoy the work: 'I was never meant to train women,' she later remarked, 'I was meant to train men'. In January 1921 she took charge of the cottage hospital in Kawhia, which was threatened with closure because of low usage and high costs. Over the following 26 years she fought to retain the hospital by encouraging an annual ball and other government-subsidised fund-raising activities. 'There was never a sale in the district', she said, 'that there wasn't a wether or a steer or something sold for me. Never one'. The money she raised enabled her to purchase, independently of the Waikato Hospital Board, extra patient comforts such as a gramophone.
The hospital dealt mainly with maternity work and accidents, but pneumonia was Reidy's speciality. Her legendary drugless cure-all was brandy, good food, laughter and fresh air. Maori made good use of the hospital and the general standard of care was praised in letters to the newspaper. The unconventional sister in charge ignored the rules for recording details of treatments and fought, with vigorous language, the authorities who wanted to close the hospital.
Widely known as 'Sister' and more familiarly as 'Reidy', she was a strict disciplinarian with a good sense of humour – a lovable tyrant both respected and feared. While restricting off-duty junior staff's relationships with young men, she released nurses for recreation and trips whenever possible.
Mary Reidy's war service continued to play a special part in her life and she was highly regarded by ex-soldiers. She was guest of honour at the Te Anga Returned Soldiers' Association ball, the recipient of toasts at the earliest Anzac reunions in Kawhia, and the first enrolled member in the Kawhia sub-branch of the Te Kuiti RSA in 1932. Later reunions took place in the hospital grounds, where she fed and accommodated the diggers. The RSA built her a retirement cottage where 'Reidy's day' was celebrated until the late 1960s.
Reidy never married, and gave away much of her income, even giving hospital blankets to patients who needed them. Over the years she kept in touch with the Mater Hospital in Auckland and always sent the sisters two turkeys for their Christmas dinner. Her contribution to backblocks nursing and the welfare of returned soldiers was recognised when she was made an MBE in 1956, and later when a room at the Te Awamutu RSA clubrooms was named after her. The novelist Mary Scott dedicated a book in which a character is based on Reidy to 'Matron MBE'.
A broken hip forced her to leave Kawhia in 1969 and move to Waikato Hospital. In 1974, with characteristic directness, she told the visiting governor general, Sir Denis Blundell, to straighten his tie: 'I can't bear to see a man with his tie crooked'. Mary Reidy died, aged 96, at Waikato Hospital on 17 January 1977. Requiem mass was celebrated at St Mary's Catholic Church, Hamilton, then she was laid to rest in the RSA section of the Kawhia cemetery. After burial, beer was provided for her old diggers, many of whom had formed a guard of honour. It was 'Sister's last shout'.