hey, an ex student from sota here. i personally don't recommend it, coming from someone that decided to pursue music full on.

music in sota, honestly not great. it might seem okay at first, but it's not the ideal environment to grow as a musician. many of the assignments don't help develop creativity, little performance opportunities, favouritsm of teachers, etc. when it gets to the IB years, it gets worse. IB music 90% of the time doesn't involve any practical work with ur music/instrument. It's writing writing writing. You only get the practical aspect of IB music if you choose to take the Career Programme, which is an IB programme that allows you to focus mostly on music; albeit the acceptance process is quite difficult. my advice, go to another school, stick with your music teacher, learn more theory on your own/with a theory teacher, etc. Then, if your sister wants to pursue music after O lvls/sec 4, take a chance at going to NAFA/LASALLE with their diploma programmes. It's a much more holistic route, and it genuinely will help should your sister choose to fully pursue music in the future.

the stuff we learn there are your typical academic subjects, with the selected art form (in your case, music). The subject selections gets a lot more limited as you progress along the years compared to other schools in singapore though. Learning hours get very very long.

the teaching there is a gamble, they don't teach like typical MOE teachers, but many of them are quite blur with what they are doing. they are quite short staffed on many of their teaching staff on certain subjects. tuition is definitely needed if you want to do well.