Thanks for the help, all, almost done with this post
After a couple iterations, this is what I ended up doing:
I had copied her home folder to a usb beforehand, with of course, older .kde4 folders. I didn't bother with other user folders, as not too important, plus I trusted they would be left alone. (After all I'm on a reliable distro).
Then I just re-installed from cd again, to sda6 root only, leaving my sda7 home intact as before.
I made a user called user4 during the prompts.
using user4, I opened a konquerer file manager as root, trashed out her .kde4 folder.
Copied October .kde folder from usb key.
Opened root terminal, and did:
#chown -R joan:joan /home/joan
Then I opened her user account, and it seemed to find itself ok.
My question now is:
Synaptic updates when re-installing OS, keeping home.
I had not the chance to export her synaptic build before the messup.
Is it ok to export the synaptic from my other machine, which likely has her apps plus a lot of mine, or just leave hers in updated mode.
I don't remember all her apps she was using except chrome, foxit reader, etc.
In any case I'll mark this solved in a bit, it is still updating synaptic at the moment, but looks good.