If she sends you a friend request, you can accept it at a time when you know she's at work or sleeping. Then you can go into your privacy options and change the way individual people see your wall.
Go into your privacy settings > customize settings > then change the "Can see Wall posts by friends" setting to "customize" and then put in that girl's name and hide what gets posted on your wall.
I've never actually done this. You should try it with someone already on your friends list. Then you can preview your profile, and a box appears that lets you type in your friend's name. Then see if it works or not
Good luck!!!