Complex sentence: In addition to his brother, Bob, Schieffer has a sister, Sharon Schieffer Mayes who became a high school principal at Keller High School at a time when only 2 percent of the principals in Texas' largest high schools were women.
Split into simpler sentences: In addition to his brother, Bob, Schieffer has a sister, Sharon Schieffer Mayes. Sharon Mayes eventually became the high school principal at Keller High School at a time when only 2 percent of the principals in Texas' largest high schools were women.