Complex sentence: Foster was born in Chicago, Illinois, but soon thereafter her father was offered an executive position with Sam Insull's Utilities Exchange Commission in Minneapolis, Minnesota where the family would soon move and where her two younger sisters were to be born.
Split into simpler sentences: Foster was born in Chicago, Illinois, but soon thereafter her father was offered an executive position with Sam Insull's Utilities Exchange Commission in Minneapolis, Minnesota. Where the family would soon move and where her two younger sisters were to be born.