Adina in Donizetti's L'elisir d'amore, Constanze in Mozart's Die Entführung aus dem Serail, Despina in his Così fan tutte, the title role in Donizetti's Lucia di Lammermoor, Olympia in Offenbach's Les contes d'Hoffmann, Philine in Mignon by Ambroise Thomas, the Queen in Die Verurteilung des Lukullus, the Queen of the Night in Mozart's Die Zauberflöte, and Zerbinetta. In 1976 Cook made her debut with the Royal Opera at Covent Garden as Gilda in Verdi's Rigoletto, and that same year returned to that house to appear as Rachel in the world premiere of Henze's We Come to the River. She also was the Fiakermilli in a new production of Arabella by Richard Strauss, with Kiri te Kanawa in the title role. In 1978 she became a member of the Bavarian State Opera where she sang regularly through 1981, when she moved to the Hamburg State Opera. She was a frequent performer with the Oper Frankfurt. During this time she added to her repertoire such roles as Catherine in L'étoile du nord, Giulietta in Bellini's I Capuleti e i Montecchi and Leila in Bizet's Les pêcheurs de perles. Cook continued to remain active in opera houses throughout Germany until 1985 when she moved back to the United States after marrying pianist Ronald Marlowe. During the thirteen years that she was in Germany she was highly active as a guest artist, making guest appearances with the Deutsche Oper am Rhein, the Deutsche Oper Berlin, the Bavarian State Opera, the Staatstheater am Gärtnerplatz in Munich, and with opera houses in Augsberg, Bern, Geneva, Hanover, Kassel, Leipzig, Nuremberg, and Stuttgart. In 1982 she sang the role of Angel of Bright Future in the world premiere of George Rochberg's The Confidence Man at the Santa Fe Opera. She also notably sang the role of The Soprano in the world premiere of Anton Ruppert's ...die Siebte at the Bayerische Staatsoper in Munich, Germany, and portrayed Tania in Luigi Nono's Al gran sole carico d'amore at the Frankfurt Opera. Cook's other international opera credits during the 1970s and 1980s include performances with the Berlin State Opera, the Grand Théâtre de Genève, and the Teatro dell'Opera di Roma among others. She also had an active concert career during these years, appearing with such orchestras as the Philadelphia Orchestra, the San Francisco Symphony, the BBC Symphony Orchestra, the Orchestre de Paris, the Hong Kong Philharmonic, the Dresden Philharmonic, and with