Dalgarno was born in Sydney in 1901 and studied medicine at the University of Sydney's Women's College. She graduated in 1925 and was hired as a resident medical officer at the Royal Prince Alfred Hospital, where she worked in the radiology department. After marrying Harold McCredie, a general practitioner, in 1928, she established a radiological practice based out of their home in Campsie.[1] Her home practice included an x-ray machine installed in the dining room and a laundry that was converted into a darkroom for developing x-ray films.[2] In 1939, she began working at the Rachel Forster Hospital in Redfern and the Renwick Hospital for Infants in Summer Hill; she also worked at the Western Suburbs Hospital in Croydon during World War II.[1]
In 1949, Dalgarno and her partner Mollie Cronin opened a new practice on Macquarie Street in central Sydney.[1] She also continued to work at the Rachel Forster Hospital, where Kathleen Cuningham had established a clinic for the diagnosis and treatment of breast lumps. Dalgarno modified an x-ray machine so that it could be used to produce mammograms (low-energy x-rays of the breasts), and in the early 1950s she performed the first mammogram in Australia.[2] In a study of 1000 asymptomatic women, she demonstrated the benefits of mammography as a screening tool to detect and treat breast cancer in its early stages, but widespread use of mammography was unfeasible at the time due to technological limitations and high radiation doses.[1][2] Dalgarno died in 1983.[2]