A lyric coloratura soprano of considerable charm, she excelled in soubrette roles in works by Cimarosa and Mozart such as Susanna, Zerlina, Despina, and in light Donizetti such as Adina, Norina, as well as Verdi's Oscar and Nannetta.
In January 1955, she first appeared at the Teatro alla Scala in Milan, in the premiere of Darius Milhaud's David, later singing Lisa in La sonnambula, opposite Maria Callas and Cesare Valletti, in the famous Visconti-Bernstein production.
In 1957, she sang Nedda to Franco Corelli's Canio in Pagliacci, and created the role of Sister Constance of St Dénis in Francis Poulenc's Dialogues des Carmélites, alongside Virginia Zeani and Leyla Gencer.
In 1965, Ratti appeared in Fedora (as the Countess Olga Sukarev), opposite Magda Olivero and Mario del Monaco, at Naples.
In America, she appeared at the San Francisco Opera, in 1958: Il barbiere di Siviglia, La bohème (as Musetta, opposite Jussi Björling), and Le nozze di Figaro (with Dame Elisabeth Schwarzkopf).