Complex sentence: Prior to writing the book, O'Donnell worked for Trump for three years, including one year as the president and chief operating officer of the Trump Plaza Hotel and Casino in Atlantic City, New Jersey.
Split into simpler sentences: Prior to writing the book, O'Donnell worked for Trump for three years. In the final year, O'Donnell worked as the president and chief operating officer of the Trump Plaza Hotel and Casino in Atlantic City, New Jersey.