Hm. The "settings" tab should show, what monitor and what VGA card is used. Could you please give us that information. "Standard monitor" can be accepeted, but it there is also something like "Standard PCI VGA card", then there is a more serious problem.
You might also check if there is an "advanced" button, perhaps some helpful options are available there.
But if I can't even get her to use her own internet tab, I doubt she would use her own account.
Well, if you have a good password for your own account, then she is forced to use her own.
Just another idea: In case you are running Windows XP or Vista, try a system restore (see Windows help for details).