The Wayne County prosecutor's office says that Camille Marino of Wildwood, Fla., will be sentenced Dec. 5.
Marino also pleaded guilty Monday to unlawfully posting a message with aggravating circumstances.
She was arrested in May after chaining herself to a library door at Wayne State University in Detroit.
Marino had called Donal O'Leary a "war criminal" and worse for using dogs for cardiovascular experiments. She also posted his address and other personal information online.
O'Leary had received a personal-protection order against Marino.
Authorities say Marino violated a campus ban by appearing at Wayne State. She says her protests were protected by the First Amendment.