One of the women apparently thought Banning "Peach Queen" winner Shanice Wilson, now 23, was having an affair with her husband.
She and three friends attacked Wilson with a carpet cutter, slashing her face and back. The attack ended her pageant career.
Riverside County prosecutors say 27-year-old Azia Aldred pleaded guilty on Wednesday to felony mayhem and assault with a deadly weapon causing great bodily injury. She was sentenced to 12 years in prison.
Twenty-four-year-old Erica Bastidas, 30-year-old Labrea Steward and 21-year-old Ariana Atkins pleaded guilty to felony assault causing great bodily injury. Bastidas got seven years, while Steward and Atkins got six years in prison.
The Associated Press contributed to this report.