33,300 results at support.microsoft.com for 0x000000F4 XP
What Microsoft says about the F4 bugcheck code
Just important to get that out there first. Why? Because after searching with Google, and sifting the results, I find that some people experience this error with bad sticks of Ram, some experience it with failing hard drives, some with motherboard issues, and at least one person with a Dell desktop experienced this because of a dead CMOS battery. No kidding, eh?
So, how do you fix it? You might not be able to. What does this mean? It could mean MANY things, and it could be caused by many different components failing and/or going bad.
For example, if this error happens when you click on or resize a window, then it might require a specific hotfix. See This MS Support Article
Now, don't go trying to get that hotfix because you think it might take care of the issue... because that hotfix only repairs that specific issue. If, for example, your copy of Windows was installed on a hard drive that was designated as "slave" (as opposed to being "master") and you are resuming from Sleep Mode, then THIS article would apply to you
At this point, you should be saying "Ok, which fix is for me, and why are you bombarding me with all this stuff? I just wanna know what steps to follow to fix it!!!!" Right?
You haven't given us nearly enough information to work with. We don't know what she was doing at the time when she got the error, aside from logging in. You have not checked the error log (Right click on My Computer, choose Manage, Click the Event Viewer, and look at the Application and System logs) for information on this and other potential errors. You have provided no specific information about the computer itself... make and model, age, hardware replacement and upgrade history, etc. Yes, all of this information is important when performing diagnostics.
You are talking about a 12 year old Operating System... which means your computer could be up to 12 years old. Which means there are multiple possibilities. You are worried about reinstalling Windows? You might be facing replacing the computer.
I will say this though. The fact that the problem has come out of the blue, and from what you have said it happens immediately after she logs into her account implies that it could be an infection.