The median time to complete the seven core subtests of the WISC-V is usually under an hour. If you add the three subtests necessary to derive the five primary indices, then it usually runs right about an hour. If you also give supplementary subtests to derive a few additional ancillary indices (QRI, NVI, etc.) it adds another 15-20 minutes or so. If you also give the phonological processing subtests, an NT student will be looking at easily 1.5 hours or more. Young high-cognitive students typically answer many more questions than expected, which is what makes the test run even longer.
Standardized conditions are a single session, perhaps with brief breaks as needed, so if there is no obvious reason that continuing would compromise performance, one usually is not expected to break up testing just because.
I usually give them permission to ask for breaks in my introductory remarks, and check in if it's been longer than an hour since the last break, or if they look like they are beginning to fatigue or lose focus. Some children really enjoy the activities, and find it rather energizing to test. If she was still happy and alert throughout testing, I would not be too concerned about score validity.
