Please by all means reward her for her cooperation with the brace by giving her this one important night off! One night off in the scheme of things is nothing. I am quite sure her orthopedist would say that was fine if you asked, also. I think this type of small concession/reward goes a long way to pave the way for continued acceptance of the brace. She will have lots of fun and get to forget about her scoliosis for one night, which is really important.
Gayle, age 46
Boston brace as a teen for AIS
Oct. 2010 fusion T8-sacrum w/ pelvic fixation, TLIF at L4/5.
Feb 2012 major A/P revision for broken rods
mom of Leah, 12 y/o, diagnosed Jan '08 with 26* thoracic JIS (age 6)
4/08 26 degrees, brace 16 hrs/day
9/08 17 deg. OOB - brace discontinued
9/09 30 deg, resuming brace
5/10 VBS Dr Luhmann Shriners St Louis
11/13 stable 3.5 yrs post-op, 15 deg
also mom of Torrey, 9 y/o son, 12* T, decreasing spontaneously (from 19*)