Her general education was received at Arlington Institute, Alexandria, Virginia. With assistance of her husband assistance she was able to complete a course in nursing at the Florence Nightingale Training School and St. Thomas's Hospital, London. In 1892 she received the M. D. degree from the Medical College of Georgia.
Her husband died in 1896 and she was left with three sons and three daughters, the youngest only three years old. During his final illness her husband, with her aid, had completed his book The Reason for the Hope, which, she said, helped to form her own philosophy of life, "Bread, Beauty, and Brotherhood. " Mrs. Barrett identified herself with the National Florence Crittenton Mission for wayward girls, of which she became vice-president and general superintendent in 1897 and president from 1909 until her death. She was also drawn more and more into other philanthropic and sociological work. She held many offices in connection with the Conference for the Care of Delinquent Children (1909), the National and International Councils of Women, the National Congress of Mothers and Parent-Teacher Associations, the Conference of Charities and Corrections, the Daughters of the American Revolution, the Commission on Training Camp Activities during the World War, and other organizations. In 1914 and 1919 she was a representative of the United States Government in Europe in connection with immigration problems.
She died, after a brief illness from acute indigestion, on February 23, 1925, at her home in Alexandria, Virginia.
Her book, Some Practical Suggestions on the Conduct of a Rescue Home (before 1904) and her chapter in Fourteen Years' Work among Street Girls as Conducted by the National Florence Crittenton Mission (1897) show her belief in friendship, work, and religion as the chief influences in rescue homes. She was opposed to separating unmarried mothers from their babies, holding that motherhood is a means of regeneration.
With all her public activities and offices, Mrs. Barrett remained a very human woman, free from the official and institutional attitude. A gentle, unaffected, yet forceful woman, she often dispensed good advice to girls in the Crittenton Homes and to mothers who brought them there. Her strong, clear-cut profile, crowned by white hair, was a familiar sight at her desk in the Mission Headquarters in Washington.
In 1876 she married the Rev. Robert South Barrett of Atlanta, for some years dean of the cathedral there, who sympathized with her desire for further education.