I agree that if she’s going to take a FL senior year, then she should suck it up and stick with Spanish. But I’d also consider emailing the admissions offices of the specific schools she’s interested in and ask whether it will be held against her if she swaps out Spanish IV for a non-audition music class. I think you’d have a more compelling case if she were swapping for an AP class or an audition only class because then it’s swapping rigor for rigor.