If you've been asked to "wipe" the disk, I suspect there is something on it that she wants completely eradicated. There are several utilities that can do this, and most can be run from a bootable CD, so you can use the one computer you have to do the job.
Here's one: Darik's Boot And Nuke
If you do a search, you'll find many more.
After you nuke it, just reinstall Windows, as normal.
You may have to re-partition the drive, depending on what program you use.