Many people think that remotely activating a web cam is some sort of high-tech maneuver. It isn't. Nanny Cams, basic home security tools, and even productivity programs like GoToMyPC can be used to spy on you with your own gear. If your girl has been around your computer, she may have had the opportunity to set up her own little surveillance system. If you're suspicious, unplug or cover up that camera, or take the action into the kitchen, away from digital recording devices.
Do yourself a favor and make sure that the only camera in the bedroom is being operated by you.