I honestly don't think its a virus.
A memory dump with loads of 0000x000 for example will be bad memory I'm sure of it.
Aim and Yahoo Messenger would do nothing to it.
Usually booting into Safemode is something the F8 button would do to, though hmm...does f12 do it too?
Get her to try new memory though. Even if it means borrowing it off you for a test run. Trust me, you might find it boots up very smoothly indeed
EDIT: If she has 2 sticks of 128mb of RAM for example, test each one individually