Tammy Lee Gibson of Puyallup pleaded guilty to assault Monday, the Seattle Times reported. She had been charged with second-degree assault and felony harassment.
Gibson, 40, went to William Baldwin's trailer last June after learning that the 24-year-old man was a registered sex offender. She said she was especially angry because she had seen him talking to her daughter months earlier.
Baldwin, who was convicted of a sexual assault on two girls when he was a teenager, was also arrested after the attack for failing to notify police that he had moved.
Pierce County Deputy Prosecutor Susan Ko said that Gibson is to be sentenced Feb. 27.
Gibson became an Internet heroine after the attack. In an interview soon after her arrest, she told the Times that she wished she had caused Baldwin serious injuries.
"I go nuts in jail, but I straight would not do anything different," she said.