O'Mahoney taught in the Lawrence High School from 1873 to 1892, filling the position of teacher of history, rhetoric and elocution, including teaching poetry to Robert Frost. At an early age she manifested unusual cleverness in recitations, and, from the beginning of her career as a teacher, a forcible and lucid way of setting forth her subject. From 1885, she was a lecturer on literary and historical subjects. She was, probably, the first Irish-American woman, at least in
New England, to venture in the role of lecturer. She began to come into prominence in the
Irish National Land League days, and made her first public appearance in
Boston at the time of a visit to that city of
Fanny Parnell. Since then, she developed as a lecturer, gaining steadily in strength and versatility, as well as in popularity. Among her lectures were "A Trip to Ireland", "Landmarks of English History", "Mary, Queen of Scots", "An Evening With Longfellow", "An Evening With Moore", "Catholic and Irish Pages of American History", "An Evening With Milton", "An Evening With Dante", "History of the United States", "The Passion Play", and "Scenes and Events in the Life and Writings of John Boyle O'Reilly". Some of those lectures were given before large audiences in the cities and towns of New England. In 1892, she delivered the Memorial Day oration before the
Grand Army of the Republic in
Newburyport, Massachusetts. She was one of the evening lecturers in the Catholic Summer School,
New London, Connecticut, in the summer of 1892. In 1892, she founded, published, and edited the
Catholic Register. She contributed to the
Boston Pilot, the
Sacred Heart Review, ''
Donahoe's Magazine, and Magazine of Our Lady of Good Counsel
. She found time to work as an original writer and compiler, and published a "Longfellow Night" and a series of school readings. She also furnished local correspondence to the Sacred Heart Review'', of Boston and
Cambridge, and was an associate member of the
New England Woman's Press Association. She was the author of
Catholicity in Lawrence (Augustinian Fathers, Lawrence, 1882);
Faith of Our Fathers (poem, Register Publishing Co., Lawrence, 1892); ''Moore's Birthday, a musical allegory
(Register Publishing Co., 1893); Famous Irishwomen
(1907), and Collection of Hibernian Odes'', 1908 (both published by Lawrence Publishing Co., Lawrence, Mass.). ==Personal life==