you need to ask her:
1) If she opened any emails from people she doesn't know
2) If she installed anything from a pop-up on a website
3) If she remembers any of the "side effects" of this happening before.
4) If she deleted any files, removed any programs or made any changes to windows
Oh... and because the average person is afraid of looking like a dork if the answer is yes, make sure she's telling the truth and even if it was unintentional, if anything MAY have happened without her really paying attention. Ask her if anything seemed kinda funny or out of place before this started happening...
Edit: also have her boot into safe mode and see if things still go awry.