Watch VoirFilms. For the first 18 years of her life, Mozart’s sister shared equal billing with her brother. Musical partners and collaborators, Wolfgang Mozart and Maria-Anna Mozart played together before Kings and Queens, and were the talk of Europe. What happened to her? Forced into retirement by age 16 because she was a woman, a stunning new investigation explores why she was retired against her will and the explosive theory: did Maria-Anna Mozart continue to compose in secret?