I agree with most of what @Hoggirl wrote above. Stanford values high achievement/excellence and passion in ECs, and the OPs daughter clearly has that in dance. A supplement - rigidly adhering to the requirements outlined - will likely be helpful, though how much is unknown. It won’t be the same as recruitment in a sport, but it will help. Double legacy certainly doesn’t hurt, either. The ACT score is the biggest question mark - Stanford is particularly known for taking who they want and ignoring numbers in favor of a “holistic” picture, but the REA applicant pool is extremely strong.