In the BIOS set up, Chanrge the boot order so that it will boot from the CDROM drive.
Put in the Windows XP disk that came with it.
Turn on the laptop. Select reinstall windows and then, when prompted, select "format drive" not quick format. This will reformat the hard drive, wiping it clean in the process.
Go through the windows install.
Once the windows install is complete, she will have to reinstall the drivers. This will be on a seperate disk labeled "applications and drivers." This will reinstall the video, audio, LAN and wirelss lan card drivers. This part is manual, done one at a time. A bit tedious.
I just went through the whole thing with my wife's dell. She got bit by a virus that got past the anti-virus software. This virus blocked all internet access to Anti-virus websites so I could not get the update and get rid of it.
If your mother is even a little computer savvy, she can handle it. Not difficult. Just a bit tedious.