Was subbing 7th/8th grade in a private school with a strict dress code. Even outerwear (sweatshirts, jackets, coats) must be school color. But that can be from medium blue to almost black/blue, so not a hardship to find a way to stay warm.
Had a teacher tell me that "Susie" got to wear her non-school color jacket one day, because she was popping out of her blouse. She had been "blossoming" and had outgrown her shirt. So, an e-mail had gone out to not fuss at Susie for being out of dress code.
I thought that was a simple was to take care of it. Respectful to Susie, no fuss, no embarrassment.
Pulling out a student for something that a dozen other teachers had already seen- I mean, if her dress was so bad, she would be sent to the office/parents called/uniform infraction, etc...whatever was deemed necessary, is just sounding like there is something weird in this relationship.
Maybe one time Lulu confided in her, and now Muffy is playing killer mommy?
(I also was jealous to hear of music assistants!)