Let me apologize for me error-I wore the brace 5 years. I get "The Brace" and dental brace time lines confused.
I went into the brace at age 11 1/2; I got out shortly before turning 16. This was a long time ago...1977 I think, so I'm sure much has changed. As you probably know, the brace is (only) to keep scoliosis from worsening--it is not for correction. In that respect it helped, but I didn't have the greatest doctor and I was given NO exercises to do when out of the brace. As a result, I had severe muscle atrophy that was never addressed. I believe now there are much better exercise programs. I would strongly encourage you to find an age appropriate Pilates program if at all possible. It will work to strengthen the core to help support the weaker back (as curved lines are not as strong as straight lines) and it will strength back muscles.
My main issue with the brace was that it ITCHED like a demon in the summer. Shower to Shower helped more than anything. My parents also had to be careful of heat exhaustion--but not overly so--as the brace not only prevented sweat evaporation, but held heat in.
If she cannot tighten the brace herself (I could not) a couple of her friends need to learn so if/when she needs to adjust the T underneath, she's have help. If there is a crease in the undershirt fabric in just the wrong place, it can be very uncomfortable and even blister.
We put an egg crate foam thing atop my mattress and that helped, but once I adjusted I found I didn't need it.
Above all, I would encourage you to not make too big of a deal of this. My parents thought it was such a horrible thing to have happen to me that we kept it secret. It would have been so much better if they'd just told my entire class, passed the brace around for everyone to see, etc. Explain it that some kids have braces on their teeth--she'll have one on her back.
Again, anything I can do to help!