So if I recall, it was just under two years ago when she was last assessed, so she would have been only about seven or eight years old. A lot of things can happen in two years at this young age, developmentally, and in terms of experience. I wouldn't perhaps go so far as to say the increase was typical, but it's also not atypical. It's within the range of changes that one does see. Interpretively, it could be that she didn't show her full potential last time, or it may be that you caught her just before one of those developmental leaps that young children in particular do have. Since they don't all have those leaps at exactly the same age, sometimes testing can inadvertently place them just on the wrong side of the leap in terms of where they fall in the age-norms (compared to the average child). It's one of the reasons testing is considered to be more stable after the primary school years.
In fairness, I do also have to caution that although they are not as sizeable as at earlier time points, there are still some score inflation effects seen with retest intervals under 24 months, so although I wouldn't throw out any results obtained in the 18-24 month range, I would have to take possible score inflation into consideration.
