There are many factors that come together to determine the level of one's ability in any given endeavor. As with anything involving many factors, statistically a few people will happen to have a lot of those factors point in the same direction, such as the direction of being able to learn piano playing very proficiently. She just happens to be way on the right side of the bell curve. Her level of passion is probably a major one of those factors. General intelligence might be another. Ethnicity might be one; is she Asian? Dexterity might be a factor. Nutrition might be another one. Nurturing parental upbringing might be one. Or alternatively, overbearing parents who force her to practice 11 hours a day. A tutor could be a factor. Having peers who are interested in piano playing or classical music could be one. Skills she honed in past lives could be a factor. People/energies she resonates with/adopts and their associated abilities could be a factor. Etc. etc.