On paper, American mezzo-soprano Isabel Leonard reads like a filly breaking free from the pack. At 25, she has already debuted at the Metropolitan Opera in Roméo et Juliette, singing Stéphano alongside Anna Netrebko and Roberto Alagna. Other star turns include her recent Zerlina with Chicago Opera Theater, a forthcoming Cherubino in Santa Fe, and a gig at the Cincinnati May Festival.