Arthur Sullivan heard the soprano while on holiday in the south of France in the summer of 1879. In September 1879, Roosevelt joined the D'Oyly Carte Opera Company and made her debut at the Opera Comique, taking over the role of Josephine during the original run of Gilbert and Sullivan's "H.M.S. Pinafore". The music critic in "The Morning Post" commented, "she has manifest talent and promises well. Her voice is sweet, sympathetic and of considerable compass, and her manner is very light and pleasant". She was then chosen by W. S. Gilbert, Sullivan, and Richard D'Oyly Carte to play Aline in "The Sorcerer", and Josephine in the first authentic D'Oyly Carte "Pinafore", at New York's Fifth Avenue Theatre, beginning on December 1, 1879. On December 31 of that year, in the same theatre, she created the role of Mabel in "The Pirates of Penzance". The "New-York Tribune" reviewed her as "certainly a pretty object to look upon; she sang creditably; she acted with zeal and good sense." "The New York Mercury", however, was unimpressed by her performance, commenting that she and her tenor colleague, Hugh Talbot, were "incapable performers", although they "failed to destroy" the opera. She played Mabel in New York and on tour until March 1880, when she left the company.