I agree with Sharon that your daughter's recovery sounds pretty normal for just 3 weeks out. She should take it very easy at this point and be careful not to overdo anything--easier said than done I know! She should be walking several times each day, probably for 10-15 minutes each time unless your surgeon advised something different. She needs plenty of rest and fluids. She needs to eat very nutritious meals to help her heal and to build her blood back up. All this takes time.
You can always call the surgeon's office to check any concerns with them, for instance if the swelling doesn't start to improve or gets worse. But right now it sounds pretty typical.
Take care, and thanks for the update.
Gayle, age 47
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, 13 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
4/15 stable 5 yrs post-op, 18* T/ 22* L, Risser 2
also mom of Torrey, 10 y/o son, 16* T, stable