My personal view is that she, and you, are working with some misconceptions. Her theater experience will be key in getting in and rigor is not as crucial in the sense of taking the top most rigor level classes. She has already exceeded the rigor needed in math and we don’t know about her science. I would continue to maximize her theater, dance, music.
Stats would be a good choice. Does she actually need math since she has done two years of calculus? Did she do geometry?
I think she should take whatever science she will enjoy. Is she interested in astronomy for instance?
The main decision for her is going to be BA versus BFA. Check out the major forum section for the best advice.
I strongly disagree with the idea that she needs a backup. First, she already has experience that pays. But more importantly, it is fine to study theater or music or art or dance at the undergrad level, regardless of eventual career outcome. These disciplines provide access to continued paths in the arts, or grad school. but also any job that requires a BA- and professional schools like med, law, nursing, business. It’s fine.
It sounds like she is in a hyper-competitive environment. It might be time to hone in on what she actually wants to do and stop worrying so much about compiling the most rigorous academic record, and do what she most enjoys academically. PM’ing you.