Complex sentence: Stevens was a guest performer on Ídolos Portugal on December 12,2010, where she sang "All I Want for Christmas Is You" by Mariah Carey and then talked with the hosts.
Split into simpler sentences: Stevens was a guest performer on Ídolos Portugal on December 12,2010. She sang "All I Want For Christmas Is You" by Mariah Carey and then talked with the hosts.