I recently installed Ubuntu in a person's computer, an older lady who
liked its simplicity and warmer feeling compared to Windows.

This person will be the only user in this computer. She lives alone and
her daughter and granddaughter only visit her twice a month or so. So
the most practical option for her is to create a single user and let it
autologin, and let her daughter use her user and options whenever she
comes round.

However, she wants to keep a diary and some other private pics and
whatnot. She would like that, when her daughter uses her computer, she
can freely browse the web and do stuff, but not access that particular
folder.

It would be handy for this kind of people who always keep a single
session open -because they're the administrators and main users of the
PC, but live with other people who use it too once in a while- and want
to keep a degree of privacy, if some folders could be "locked" so that
Nautilus would ask for the user's password in order to be able to open
them.