Oh dear God, unless you'll be using a bash prompt, don't install Linux on a machine that old. And especially not KDE.
Wipe the machine and install Windows 2000 on it. If you want, you can use nLite to remove IE and other shit from the install. Then make her use Opera or Firecox. On a machine that old, preferably Opera.
Well, that's what I'm saying. I don't want to install a Linux system on her machine, just use xdm or something so she can use my computer. I'm just not sure how to go about setting that up.