Her parents were Joe Jefferson Estill, who was a civil engineer, and Irene Shook, who was an English teacher in a High School before marrying Joe. Mary Ellen's family was a fairly typical middle-class Presbyterian one and for ten years she was an only child, until her younger brother was born.
Ang kanyang mga magulang ay Joe Jefferson Estill, na isang civil engineer, at Irene Shook, na noon ay isang English teacher sa isang Mataas na Paaralan bago marrying Joe. Mary Ellen ng pamilya ay isang pangkaraniwang pantay gitna-class Presbiteryano isa at para sa sampung taon na siya lamang ay isang anak, hanggang sa kanyang batang kapatid na lalaki ay ipinanganak.