When Duffy learned that Westminster Choir College's program in choral conducting was not available to undergraduates, she began to study vocal performance under professor Laura Brooks Rice, who became her mentor and continued as her voice coach after college.
She has sung at the Tanglewood Music Festival as Despina in Cosi fan tutte by Mozart, and as Tebaldo in Don Carlo by Verdi, both with conductor James Levine.
[3] Contemporary works in which Duffy has appeared include Neither by Morton Feldman at the Wien Modern festival, The Ghosts of Versailles by John Corigliano, and the American premiere of What Next?
[6] In September 2016 she premiered the role of Bess in Missy Mazzoli and Royce Vavrek's opera Breaking the Waves.
She received unanimous acclaim with Fred Plotkin of WQXR proclaiming her turn the "performance of the year.