Actually, the movie is based on the Broadway show, so the ABBA music was not just thrown in as a second throught. That's just incase nobody knew about it. And yes, Amanda Seyfried played Karen in Mean Girls. This is actually her first big movie role, I believe. Yeah, Mean Girls was huge, but she was still sort of an unknown and did not have very many speaking lines. She was also in Alpha Dog, but that movie was bad.