Sister Mary Peter McCusker (Lois Jean) was born on July 10, 1937 in Sisseton, South Dakota on the Lake Traverse Indian Reservation. Her parents, Lewis J. McCusker and Doris Owen McCusker had five other children: three boys, Bob, Norman and Tony, and two other daughters, Marie and Nancy. When Lois Jean was fifteen, the entire family moved to Modesto, California and a few years later, Sister Mary Peter graduated from Downey High School. She spent a year at Modesto Junior College before enrolling in nursing school at St. Mary’s College of Nursing in San Francisco. She earned her R.N. in 1959. In the summer of that same year, Lois Jean entered the Sisters of Mercy in Burlingame and, in 1962, professed her vow and took the religious name Sister Mary Peter.

For eleven years Sister Mary Peter worked as a pediatric nurse at St. Mary’s Hospital in San Francisco, then at Mercy Hospital in San Diego. She went on to Catholic University in Washington, D.C. to earn her Master of Science in Nursing with an emphasis on child and family practice. For three years, she was a faculty member at the University of San Francisco School of Nursing. From 1979 to 1984, Sister Mary Peter served the impoverished communities in the Altiplano in Puno, Peru, the area in west-central South America where the Andes Mountains are at their widest. Upon return from the mission, she ministered as a staff nurse for the Visiting Nurse Association of San Mateo County and for the Home Health Care Department at St. Mary’s Hospital for four years. In 1991, Sister Mary Peter began a health-based ministry to families in the Hispanic community at Most Holy Trinity Parish in San Jose, California. This program provided health information and services to parents and their children. She became more cognizant of the needs of the community and in 1993, she along with Dan Germann, SJ opened the Day Worker Service Center to immigrant workers who would stand on the roadways and wait to be hired for the day. The Center also provided other services like ESL classes and different women’s aid groups. In 1999, Sister Mary Peter was named Woman of the Year for the 13th Congressional District by Senator John Vaconcellos. She was recognized for her work in providing health care and employment opportunities. In 2010, Sister Mary Peter retired from active ministry and spent her last years at Mercy Retirement and Care Center in Oakland, California. She died in Oakland on December 6, 2016 at the age of 79.