I would think that since she’s getting offers from professional dance groups and UCLA, that her dancing is likely good enough to stand out as distinctive to Stanford admissions. How much they’ll care about/weight that I don’t know.
FWIW though Stanford is conscious of getting its fair share of humanities and arts students as it does not want to be known just for CS, and I notice a definite tendency to showcase students who are singers, musicians etc. at Stanford events.