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 49
Oct 2010 fusion T8-sacrum w/ pelvic fixation
Feb 2012 lumbar revision for broken rods @ L2-3-4
Sept 2015 major lumbar A/P revision for broken rods @ L5-S1
mom of Leah, 14 y/o, Diagnosed '08 with 26* T JIS (age 6)
5/10 VBS Dr Luhmann Shriners St Louis
5/16 6 yrs post-op, 24*T/ 22* L, mild increase in curves, checking bone age
also mom of Torrey, 11 y/o son, 16* T, stable