An animal rights activist’s defamation lawsuit against a fellow activist has boomeranged with a judge dismissing her case while allowing her rival to pursue a counterclaim that she had been libeled.

Both the plaintiff, Kiley Blackman, a court officer in the Bronx, and the defendant, Barbara Stagno, were involved with two animal rights organizations in Westchester County — People for the Ethical Treatment of Animals and In Defense of Animals — Blackman as a volunteer and Stagno as an employee.