How do you delete a computer off of your wireless network connections?

My co-worker connected her personal laptop to our business router. Now on our business computer, instead of showing the connection strength bars, it shows a small computer with what looks like a pitchfork coming out of it. When we click on it, her name (BRITTANY-PC_Network) shows up under wireless network connections. We've been trying like crazy and can't figure out how to get it to go back to the way it was. Help!