 O'Mahoney was one of the first Catholic women in New England, if not in the United States, to speak in public from the platform.Among her lectures may be mentioned "A Trip to Ireland" (illustrated); "Religion and Patriotism in English and Irish History" (illustrated); "Mary, Queen of Scots", and "Joan of Arc" (both illustrated); "An Evening with Milton, including recitations from Paradise Lost", illustrated with fifty views from Dore; "An Evening with Dante, including recitations from the Divine Comedy", illustrated by seventy-six views from Dore; and "The Passion Play of Oberammergau".She founded, and until marriage, edited and published "The Sunday Register" (Catholic weekly).