If it is due to an intermittent blockage, a scan may not help unless she is so lucky as to get the scan at just the right time (has never worked for our kid, really a pain). Definitely encourage her to raise intermittent shunt troubles as a concern to her neurosurgeon and ask them how they'd like to follow up. And maybe call them every time it happens (and track them on a calendar to see if there are other patterns). Someone on hyceph-l may have a better suggestion.