Let her choose her senior classes! With the middle school course she has the 4 years of SS. Four years of a foreign language will make her competitive- only take the next year if she wants to. Let her try something for the fun of it as a HS senior!
Son took first semester AP Music Theory as a sophomore when the computer course wouldn’t fit his schedule, his cousin who got a music performance degree in college had to do the course (both semesters and the AP exam) as independent study in her HS. She had a scholarship for the music in college.
Music and math go together so logical for a STEM type student. The art class will be something she is unlikely to take in college whereas the music theory material likely is covered in part through orchestra. I would opt for art based on your info here- and not worry at all about the potential grade. A nice change from the academics (as is orchestra).
It looks like she has done well academically and with courses taken to date. Time for the luxury of a totally unneeded course just for something different she is unlikely to do later. Great for her to have such options.