[2] Horn, an outspoken member of the American Library Association's Intellectual Freedom Committee, worked at Bucknell University in Lewisburg, Pennsylvania, in the early 1970s.

Horn was jailed for nearly three weeks for contempt of court after refusing to testify for the prosecution in the 1972 conspiracy trial of the "Harrisburg Seven" anti-war activists.

[5] She emigrated with her family to Canada in 1926 at the age of 8, then to New York City[5][6] where she attended Brooklyn College and the Pratt Institute Library School.

[7] Berrigan, a Roman Catholic priest and anti-war activist, was serving a sentence in a nearby federal prison for burning draft files concerning the Vietnam War.

[6] Berrigan, from his jail cell, was alleged to be plotting along with six other individuals (Harrisburg Seven), to blow up heating tunnels beneath Washington, D.C., and to kidnap Henry Kissinger, the national security adviser to President Richard Nixon.

[7] In addition, Horn was anti-war and claimed that "...the defendants, had been taking whatever steps presented to themselves to stop the killing in Vietnam and the brutalization of people that comes with war.

Horn was jailed for almost three weeks,[9] "for refusing to testify for the prosecution in the sensational trial of anti-war activists accused of a terrorist plot.

At first, the American Library Association's executive board refused publicly to support Horn's stand against the government's attempts to intimidate and silence Vietnam War protesters.

"[7] Eventually she was given assistance by the association's Social Responsibilities Round Table, as well as the Leroy Merritt Humanitarian Fund and the Freedom to Read Foundation.

Judith Krug, longtime director of the American Library Association's Office for Intellectual Freedom, has called Horn "the first librarian who spent time in jail for a value of our profession.