[4][5] She became a Young Artist with the Palm Beach Opera when she was fourteen, and made her operatic debut there two years later as the Sandman in Engelbert Humperdinck's Hansel and Gretel.
[9] In January 2016, she performed at Venice New Year's Concert with Stefano Secco,[10] and at Milan's fabled La Scala as Gilda in Rigoletto with Leo Nucci.
[11][12] In January 2017, she sang in the New Year's Concert at Palermo's Teatro Massimo, followed in March by six performances as Ilia in Mozart's Idomeneo at the Metropolitan Opera in New York.
Her 2017/2018 highlights include Susanna in Mozart's Le Nozze di Figaro at The Metropolitan Opera, solo recitals in Dallas and New York City, a tour with Andrea Bocelli, Nannetta in Verdi's Falstaff at the Staatsoper Berlin, and Norina in Don Pasquale at the Opéra National de Paris.
In 2022, her Violetta in the Metropolitan Opera production of La Traviata was hailed as showing Sierra's "innate sense of style and line that recalls Italian sopranos of the past, with decadent rubatos that fall on just the right side of indulgence.