So, copy the contents of her home directory to a DVD, including hidden files. Reinstall Kubuntu with a separate Home partition, copy the files back and it should be fine. Only copy documents, music, videos and thunderbird and firefox, let the rest be rewritten in the install.
If she already has a separate home partition then boot into Gnome and delete the .kde folder, then restart with the Kubuntu install and format / but not /home and you should end up with a stable system. I would still backup the .thunderbird .firefox and music videos and documents just in case.