Complex sentence: Within the School District of Philadelphia, she attended the historic Masterman Laboratory and Demonstration School as well as the Philadelphia High School for Girls--serving as her high school President her senior year and Vice President her junior year.
Split into simpler sentences: Within the School District of Philadelphia, she attended the historic Masterman Laboratory and Demonstration School as well as the Philadelphia High School for Girls (PHSG). At PHSG, she served as high school President during her senior year and Vice President during her junior year.