[1][2] Mary Eileen, the second of three children, moved with her family to Spencer, Indiana, at the age of ten.

As a condition of the political compromise that was reached, she agreed not to seek reappointment as state librarian.

[3][4] At the thirteenth annual meeting of the Illinois Library Association, when Ahern was serving as the organization's president, she delivered the annual address with these words of encouragement: "We are librarians because we feel that in these lines there are greater opportunities for helpfulness, greater vistas of optimistic outlook, greater results in actual returns of the worthwhile, than in any other line of work which we might have chosen.

"[7] Ahern also served in the federal government and as secretary of the Library Department of the National Education Association.

During World War I she served as publicity agent and distributed books for the U.S. military in France from January to July 1919.

[1][8] Ahern is best known for her widespread influence in establishing and strengthening connections between libraries and schools in the United States.

She was also an advocate for women in the profession and saw the potential of libraries to provide lifelong educational opportunities to the public.

[3] As the British librarian W. C. Berwick Sayers described her: "How intensely alive Miss Ahern seemed, how full of ideas, ideals, enthusiasms, how enquiringly humorous!