Sullivan was sent to Paris, in 1889, as special cable correspondent of the "Associated Press" for the Universal Exposition. At its opening ceremony, she was the only writer to whom a seat was assigned in line with the French president, and the only representative of the press thus invited to assist at the ceremony. She was an authority on art, literature, science, politics, music and economics. Naturally gifted as she was, her remarkable power of concentration and the intense tenacity with which she applied herself made it easy for her to master any subject to which she devoted herself. Sullivan's "Ireland of Today" reached a sale of 30,000 copies. She co-authored "Mexico, Picturesque, Political and Progressive" with Mary Elizabeth McGrath Blake, of Boston.