I cannot begin to imagine what she could do to cause this. If you want to update the OS, slap in the OSX install disc and reinstall OSX - it will update automatically after that.
Actually I just thought of something:
I once porked my OSX installation totally by following windows logic - I checked file permissions on my drive after updating the hdd and saw I wasn't the owner on many things. If you take ownership to the files and override the original rights you'll hose the whole OSX good. If you did that then it's reinstall time.
Yeah, you say it takes 3 clicks and a few seconds? Uh, huh, then why is it her computer has been dead for almost a week now? It it was Windows, I would have wiped the drive and re-installed the OS and had her running in an hour, or so.
I was talking about windows in a virtual host there Roy. You can have her OSX sparkly shiney by inserting the OSX install DVD and restarting the computer holding c key at startup. Optionally you can hold the option key at startup at which time you can choose to boot from a recovery partition (necessary on some newer macs). If she has OSX Lion, then
http://www.apple.com/macosx/recovery/ helps
No one at Apple has been any help, at all. And see, that is where the biggest issue lies with Apple products. They are fine, until they are not fine, then you are pretty much screwed unless you pay Apple a ton of money for support. If that perception is incorrect, then Apple needs to work on it.
I would just try to reinstall the OSX first. You'll be prompted to either create an account or sign in after the basic setup. The iforgot site will guide you through if she already did one.