My daughter is 11, but had a similar situation last school year. I ended up going and talking to her teacher about it. We decided it would be best if she just told the whole class.
It ended up working! She did a show-and-tell presentation about scoliosis and about her brace and some kids even tried on her brace to see what it felt like. I think it gave them a better understanding about why she is having to wear the brace and it let them ask questions in a controlled environment. This was all last February and she hasn’t had any issues since.
Hope it helps,