From The Smithsonian:
“Virtuosic.” “A prodigy.” “Genius.” These words were written in the 1760s about Mozart—Maria Anna Mozart. When she toured Europe as a pianist, young Maria Anna wowed audiences in Munich, Vienna, Paris, London, the Hague, Germany and Switzerland. “My little girl plays the most difficult works which we have … with incredible precision and so excellently,” her father, Leopold, wrote in a letter in 1764. “What it all amounts to is this, that my little girl, although she is only 12 years old, is one of the most skillful players in Europe.” The young virtuoso, nicknamed Nannerl, was quickly overshadowed by her brother, Wolfgang Amadeus Mozart, five years her junior. But as one of Wolfgang’s earliest musical role models, does history owe her some measure of credit for his genius?
“That’s a very interesting question,” says Eva Rieger, retired professor of music history at the University of Bremen and author of the German-language biography Nannerl Mozart: Life of an Artist in the 1800s. “I’ve never really considered that possibility, and I don’t know of anyone who has before.” Such a suggestion may seem far-fetched to Mozart fans and scholars. “To answer the question of how much Nannerl influenced Wolfgang musically, I would say not at all,” says Cliff Eisen, professor of music at King’s College in London and editor of the Cambridge Mozart Encyclopedia. “I’m not sure there is evidence that the dynamic was in any way exceptional beyond what you might think between one relatively talented musician and one who far outshines the other.”
More here.