That model was an impromptu hire by CM's management for that shoot. We (her fans) were online chatting with CM's people on her website, and they actually asked if we would like to see CM shoot with girls. Of course we said yes, so they hired her for the quickly upcoming shoot. As you can see, the model hated every minute of it, so I think she never came back.
Without the chat on the CM.com website, I doubt Christina would've ever even gone nude. She went nude because some of us fans submitted scripts for her to act out. Her first nude scene came from a fan's idea (I won't say who... wink) for the photographer to shoot her nude in the reflection of a mirror (you know how shy she was). She went nude in that first vid in front of a mirror on a clothes dresser. I think the name was Reflections, or something.