So we are looking at the same situation, and also went through something similar with previous children. Most state university systems have online asynchronous courses either at the 4-years or 2-year community colleges that should get her through diff eq and linear algebra. My suggestion would be to look into dual enrollment online through your state higher ed system, as those are more likely to have transfer value in the future, and also are more likely to be taught by actual professors. Of course, in-person at the 4-year is the most likely to be high quality, but if the objective is to keep her interested in and progressing in math, it's still likely worthwhile even if the online courses don't turn out to be quite at the same level.
I would also note that taking college courses is likely to be at an intructional pace that suits her better. High school pace is about half-speed vs college, which can get frustrating sometimes.
This would be a good conversation to have with her school counselor, in addition to your own research on dual enrollment in your area. Sometimes there are articulation agreements between high schools and colleges already in place. I know that several of the states have established dual enrollment programs for CCs that are discounted for early learners.
We have multiple musicians too, and have also encouraged them to keep multiple directions going. There's a lot of overlap between STEM and music minds.
