How do I remove player in LBP?

[Augustine864]

I can't seem to figure out how to remove a player while in Little Big Planet. Sometimes I will play with my sister and her boyfriend buy, (like last night), my sister will eventually want to stop and just watch. In this case, how do I remove her from the game without quitting to the XMB and then re-launching? I figured that option would fall under "Manage Players" when I hit start, but there is always a line through it and I can't select it, (online only?).
I also thought that if i just turned off her controller that would take care of it, but I can no longer figure out how to turn the controller off now that the PS button takes you to the XMB.