Complex sentence: Burnett attended St. Andrew's School, a private co-educational college preparatory boarding school in Middletown, Delaware, graduating in 1994, to which she returned in 2009 to deliver the commencement speech.
Split into simpler sentences: Burnett attended St. Andrew's School, a private co-educational college preparatory boarding school in Middletown, Delaware, graduating in 1994. She returned to the school in 2009 to deliver the commencement speech.