Well, she's going to notice when she can't get to it. But, that's beside the point I guess.
Assuming you have a router you can block the site from there. Or just add it to the restricted sites in IE. Tools => Internet Options => Security => Restricted sites.
"i would never use a firewall, even without a router protecting me. Firewalls are just wastes of memory."
name omitted to protect the innocent
the cake is a lie