The restarts were fairly infrequent -- once every couple of days or so -- but it's happening more often these days. In fact, it just happened three times in a 5-10 minute span.
It used to happen when she played games online, but they were flash games and not anything really large. Over the past few days it's been happening on random websites, and even when she wasn't browsing the internet at all. In fact, I had her download ewido, but it restarted during the scan!
I also read that it could be because the laptop is overheating. I felt the base and the bottom of it when it restarted, and it didn't feel exceedingly warm.
Also, I should mention this: she used to have almost this exact same problem many months ago (the difference being back then, her computer would shut down rather than restart). She plugs her laptop in (as opposed to using the battery). We figured out that the prong that connects the adapter to the laptop was loose, so we sent it in and had it replaced. That seemed to fix the problem, until now.
Anyway, I am not entirely sure what the next step should be or how this can be solved. Any help would be appreciated. Thanks!