After the Grantala's return to Sydney, Constance reenlisted in the Australian Army Nursing Service (AANS)(AIF) on 24 July 1915 as a Sister. She departed Australia on RMS Orontes, departing Sydney on 31 July 1915. She was allocated to No 1 Australian General Hospital (AGH) Reinforcements.
After arriving in Egypt, Constance was attached to No 3 AGH at Abbassia (near Cairo). In August 1916, she embarked as a passenger on HMAHS Kanowna for England, where she was attached to No 1 AAH at Southall and then at Queen Mary’s Military Hospital at Whalley, Lancashire.
She returned to Australia on the HMAHS Kanowna, as part of the nursing staff, arriving in Sydney in March 1917. Her AANS appointment was terminated (“for the purposes of marriage”) on 25 March 1917. She married Henry A.S. Holliday in April 1917.