I thought Microsoft was still providing security updates to XP, just not any bug fixes. Anyhow, yes. You will have A LOT of trouble finding drivers for XP.
If the new PC has a touchscreen, stick with Windows 8 and help her find some tutorials. Otherwise, Windows 7 and show her how to search in the start menu for things.
Any computer, no matter how old, can serve a meaningful purpose.
Behind every closet door is a dusty computer waiting to be reborn.