Sr. Mary Estelle was a great-granddaughter of Myles Cunningham. She was born Margaret Cunningham in 1898 in Kilbaha, Newtownsandes (now Moyvane), Co. Kerry. Her parents were Richard Cunningham and Brigid Dore.

At the age of 17 she and her older sister Johanna joined the Sisters of St. Joseph in Concordia, Kansas where a distant relative, John Francis Cunningham, was a bishop.

Sr. Mary Estelle worked as a nurse for many years at St. Joseph's Hospital in Belvedere, Illinois where she died in 1987 aged 89.

Johanna, Sr. Mary Estelle's sister, became Sr. Mary Ellen and worked in El Paso, Texas for a time before moving back to Concordia to work in St. Anthony's Hospital there. Sr. Mary Ellen died in Concordia in 1989 aged 93.