Can you block someone from reading your wall if they are in your network but not your friends list?

Say I have a public profile on Facebook, which means anybody at my school can see my photos, info, and wall posts. "Cindy" is not one of my friends but she's in my network, so she can see this stuff. But, I talk about "Cindy" every now and then with my friends so I don't want her to see my wall. Can I block her somehow only from reading the wall, but still keep the profile open to other networkers and my friends? The trick is, I go to the "Customize" option under "Settings"->"Posts by Friends", but I can only add someone to the block list if they are already my friend.