Neuropsychological assessment attempts to diagnose and define the neurocognitive effects of medical disorders that have a direct or indirect impact on the brain. This type of assessment is appropriate in several circumstances: to detect neurologic conditions via quantitative assessment of neurocognitive abilities, to address differential diagnosis between psychogenic and neurogenic symptoms, to delineate the neurocognitive effects of central nervous system disorders, to monitor the recovery or progression of central nervous system disorders.
In general, what we are attempting to achieve via neuropsychological testing is an understanding of the relative contribution neurological factors have in the symptom picture that is being observed. In your daughter's case, my sense is that her therapists want to determine if there are particular neurological deficts that might be contributing to her problems. Sometimes, children with sensory integration difficultires can have a perfectly normal neurological examination and negative findings on neuropsychological testing. Likewise, such children may display identifiable neurological conditions (either as part of, or alongside, the sensory integration problems), and it is important to determine this. Thus, for your daughter, the focus seems to be much more on the neurological aspects of her functioning than on the mental health aspects.