McPhee, a fan of the Web-based series, approached the creators about participating in an episode, American Digital Networks said in a release on behalf of the creators.
McPhee plays a character, not herself, in the video blog on Friday. A song from McPhee's soon-to-be-released self-titled debut album can be heard in the background of the "Lonelygirl15" installment.
"Lonelygirl15" centers around Bree and other characters with their own chains of video blogs. The characters interact and the plot lines are woven together to produce a single, all-inclusive tale of the character's videos as they investigate messages embedded in the clips.
"Lonelygirl15" has its own Web site and is posted on YouTube and other sites.