Complex sentence: She is the first person with a medical degree to lead any Planned Parenthood in the United States, having filled the vacancy left by Marty Walz, who resigned from the position in January 2015.
Split into simpler sentences: She is the first person with a medical degree to lead any Planned Parenthood in the United States. She filled the vacancy left by Marty Walz, who resigned from the position in January 2015.