My computer has a bit of a bug problem, or something as well. Namely that it'll randomly restart whenever I'm in the middle of typing something, whether that be an e-mail, an lj post, or a word perfect document. I've yet to figure out what makes it do that, but I still keep cleaning it up often with adaware and AVG (does your sister have those?) they're the best free anti-virus whatchamawhosits I've found. Adaware is especially useful I think. If she can't d/l those however, make sure she doesn't have anything she wants on her computer (unlikely) then wipe it, and reboot with a windows whatever disk. Worked for me a couple of times. However, there's that whole catch of those files you'd die upon losing...so yeah...

cheers