Mabel was born in Queensland, the youngest child of Hugh and Matilda Campbell. After training at the Coast Hospital in Sydney she worked at the Inverell District Hospital before becoming part owner of the Private Hospital known as ‘Craignish’.
At the age of thirty one Mabel enlisted with the AIF in August 1915 stating her next of kin to be her sister Mary, Matron of Inverell Public Hospital. During World War 1 Mabel was the first Inverell woman to be given an official public farewell and to be presented with the inscribed Inverell Medal. The Mayor, on behalf of the community, also presented Mabel with a purse of Sovereigns and a rug.
Mabel sailed from Australia in 1915 on the ship RMS Morea with the 10th Australian General Hospital Unit. Upon arrival in Egypt she transferred to the 1st Australian General Hospital in Cairo. After becoming ill at Heliopolis she was returned to Australian and upon arrival in Melbourne in May 1916 she was discharged due to ill health.
Two years later Mabel married Englishman Rev. John Cuthbert Nankivell in Melbourne and they went to live in England.
Nurse Campbell has her name recorded on the St. Andrew's Presbyterian Church Honor Roll at Inverell.