In 1837 Frezzolini made her professional opera debut in the title role of Bellini's Beatrice di Tenda at the Teatro della Pergola in Florence. She quickly arose in major opera houses throughout Italy, often in the operas of Bellini and Donizetti. In 1838 she was heard at the opera houses in Siena and Ferrara. In 1839 she portrayed the title role in the house premiere of Saverio Mercadante's Elena da Feltre at the Teatro Comunale di Bologna.[1]
She sang several more roles in Bologna in 1838–1839, including the title roles in Anna Bolena, Beatrice di Tenda, and Lucia di Lammermoor. She made her debut at La Scala in 1839 as Bianca in Mercadante's Le due illustri rivali.[2] She also made her debuts that year at the opera houses in Pisa, Reggio Emilia, and Perugia.[1]