Ahh good olle parental setting.
I found this.
Allows time restrictions to be applied to services and user ...
the account has expired or the user is not allowed to log in at this time of day
DansGuardian 2 web content filtering
DansGuardian is an award winning Open Source web content filter
You can also configure firefox and thunderbird to use a proxy server that filters content for kids.
You could also make up a simple cron job under her account that checks the time and logs here out at what ever time.
and logs well you could do a lot of things with the logs ill come up with a simple monitering salution.
Thanks for asking this question gave me something differant to do
Ill keep searching and learning untill you have the answers and salutions to your problems.