Yes, it may be quite common to experience more pain, as there is quite a bit of Trama involved with this type of surgery.
A fusion can be a very long recovery as well, and it is important for her to follow the Dr's instructions to a "T"
It will get better over time, and tell her not to get discouraged, as she may have some bad days and good days, for quite some time. It is also important that she stay ahead of the pain, by taking the meds like she is supposed to. I can tell you that, I never had to be reminded to take them.