I think the OS and the atlas program are taking the most room. If you know the name of the program, just do a simple search for it. If there are things she wants, back them up to floppy disks (I doubt a computer like that has a burner) and erase the hard disk. I hope she has the original OS disk with her or your toast if you erase it on the HD. You could use your copy of Windows (as long as it's not XP) but that's piracy and Bill Gates will hunt you down to the ends of the earth. 

She also has the choice of buying a larger hard disk, they've come down in price significantly. That's her choice though. 

Hope this helps a bit.
Orenda

Did you take out the hard disk - check the jumper settings are not clipping the drive at a lower disk allocation.

PC

this may sound rather stupid but have you emptied the recycle bin... forgive me if you have but if you delete something the free space will not appear until you have emptied it....happened a while back same sorta thing but he hadnt emptied it lol