In 1962, she traveled to Geneva, Switzerland as part of a Women Strike for Peace delegation, protesting the effects of nuclear testing on children's health.
Also that year, Knopp became a Quaker, serving as a prison visitor in the Federal penal system through her designation as a "minister of record."
In 1968, with Bob Horton, Knopp co-founded Prisoner Visitation and Support to further that work, focusing initially on the increased number of imprisoned resisters to the Vietnam War.
The program's goal was to offer sex offenders treatment through an international referral system to break the cycle of behavior rather than focus on punishment.
"[10] Dutch criminologist Herman Bianchi remembered Knopp as a "Mother Teresa among abolitionists.