Lytle was born in San Antonio, Texas, and received a bachelor's degree from Incarnate Word College there in 1943.

She married John F. Killea in 1946, and left the CIA in 1958 when her first child was born and when her husband was named consul general in Monterrey, Mexico, by President Eisenhower.

John was subsequently named consul general in Tijuana, and Lucy remained interested in U. S.-Mexico relations, helping to found, in San Diego, Fronteras de las Californias and the International Community Foundation,[2] "both of which sought to help people south of the border through grants and charitable giving."

Controversy surrounded the election as Leo Thomas Maher, the Catholic bishop of San Diego, prohibited Killea from receiving communion because she was pro-choice; she was the first politician to be punished in such a way for her political views.

She was a senior fellow of the International Community Foundation,[10] and served on the Board of Advisors of the San Diego–based Center for Ethics in Science and Technology.