I feel like I'm playing Devil's Advocate here. I'm much more libertarian (small L) than conservative, but we see eye to eye about most school issues.
So, here is one reason why the choir teacher should not (just) advise the student to tell her parents: Telling her parents would have been the logical move for any kid who is molested/assaulted/raped at school. They might tell the school first if they are in a hurry to report it, but most kids would think "I'm telling mom," right off the bat.
Therefore, if she has not told her parents, there is likely a reason. Maybe a good reason, maybe a dumb reason, maybe a borderline reason. Rather than try to work all that out, the obvious move for the teacher would have been to report it.
It sounds as if she did report it, but to her superious rather than CPS. Her superiors did not follow the law and let CPS know. Unfortunately, that teacher also did not follow the law, if the law in her state requires that CPS, not just the bosses, be informed. I get the reluctance to get involved, and feeling that principals get paid extra to deal with exactly that kind of thing. You're trusting them with your career, your reputation, and maybe your freedom when you leave it to them.
Lawmakers know that some administrators would prefer to keep something like that quiet, so they require everyone who works with children to report it. It would be a travesty if that teacher lost her license, or served time. It really should be part of the start of year trainings we get like "blood borne pathogens," and "Run, Hide, Fight."