From whom are you getting recommendation letters from?

All the schools that I’m interested in applying only require one recommendation letter, but they allow optional letters. My main recommendation letter is obviously from a professor, but I was wondering if music teacher from high school would be acceptable as a transfer recommendation letter. She knows me on both academic and personal level, but I don’t know if recommendation letter from high school will be much of a help or if the admission committees will even prefer it.

The music teacher sounds like a solid additional letter. They may want something more current for the primary letter.