Complex sentence: She had auditioned when she was in the 6th grade, and traveled to the U.S., where she trained for 6 years, but came back in 2008 to continue activities in Korea.
Split into simpler sentences: She had auditioned when she was in the 6th grade, and she traveled to the U.S., where she trained for 6 years. She came back in 2008 to continue activities in Korea.