Complex sentence: Cassidy worked as Editor-in-Chief of "Prevention Magazine" from 2000-2003, and was responsible for creating and producing the largest health publication and 14th largest magazine in the United States.
Split into simpler sentences: Cassidy worked as Editor-in-Chief of "Prevention Magazine" from 2000-2003. She was responsible for creating and producing the largest health publication and 14th largest magazine in the United States.