Ok, the combination of ballet + STEM makes more sense to me now. She will need to clearly explain this in her apps. But it sounds like she is a good writer and will be able to handle this.
Regarding the ‘packaging’. Even though she attends a private K-12, her guidance counselor is not always the best to rely on. The goals for a GC at a private school are to maximize placements for the entire class. Not to maximize individual chances for your daughter. There is a lot happening behind the scenes. So this is why I suggest that you seek outside expertise on the packaging. Find a good consultant/college counselor. Paying for a few hours of advice is well worth it, especially since it sounds like you can afford full tuition.
My son went to Lawrenceville, and about 1/3 of the class ended up at T20 schools. The college counseling office was very good at what they do. But I still think its worth getting outside advice.