Is it normal after scoliosis surgery to have a late period or different cycle?

Technically no. There is not a direct relationship between scoliosis surgery and having a late period. It is possible an indirect effect of anesthesia or the "stress of surgery" may have played a small role. Do check with your Ob as early on and with stress periods are subject to have variability. In the meantime, exercise and Pilates for core strengthening may help.