The year 1992 was one of major debuts for Frittoli, during which she appeared in Carmen in Philadelphia, in Naples in La Bohème, at La Scala in Milan in Beatrice di Tenda, and at Santa Cecilia in Rome in a rare production of Schubert's Rosamunde. The next year she played in Carmen (Micaëla) and La Bohème (Mimì) at the Vienna State Opera and made an impression in Baroque opera in Pergolesi's Flaminio at the Teatro San Carlo in Naples.
Mimì and Micaëla were her roles in her first season with the Metropolitan Opera in New York, and she was Micaëla when she sang at the Royal Opera House, Covent Garden in London.
She has also appeared in Ferrara, La Monnaie in Brussels, the Opéra Bastille in Paris (as Donna Elvira in Mozart's Don Giovanni), the Teatro Communale of Florence, and the Regio of Turin. She toured with the Maggio Musicale of Florence as Liù in Puccini's Turandot when it took its spectacular production to China. This included the famous performance known as "Turandot in the Forbidden City," which has been recorded under Zubin Mehta's direction as a compact disc and a DVD on the RCA label.
Other leading operas in her repertory include Le nozze di Figaro (Countess), Così fan tutte (Fiordiligi), La Clemenza di Tito (Vitellia), Otello (Desdemona), Falstaff (Alice Ford), Il Trovatore (Leonora), and Simon Boccanegra (Amelia). She was invited to participate in the opening production of the renovated Royal Opera House in London in 1999 as Alice Ford.
Conductors with whom she has worked in opera and on the concert stage include Claudio Abbado, Lorin Maazel, Sir Charles Mackerras, Riccardo Muti, Georges Prêtre, Daniele Gatti, Antonio Pappano, Sir Colin Davis, Sir Andrew Davis, Semyon Bychkov, and Riccardo Chailly. In the year 2000, she added to her credits the parts of Sifare in Mozart's Mitridate, rè di Ponto and Marghereta in Gounod's Faust. In addition to the Forbidden City discs, her recordings include Puccini's Il Trittico on Decca, Il Barbiere di Siviglia on Teldec, Il Viaggio a Reims on Sony, Pergolesi's Stabat Mater on EMI, and Rossini's Stabat Mater on Decca. She is also in demand as a concert singer, where her repertory includes Strauss' Four Last Songs, Mozart's D minor mass, K. 427, the two versions of the Stabat Mater already mentioned, Verdi's Requiem, and Brahms' German Requiem in addition to a concert performance of Offenbach's Tales of Hoffmann. She appears frequently as a recital singer.