Peniche was born in San Diego, California on March 20, 1984. Her mother, Lee Ann Rosenbarger, is a Business consultant. Peniche has two younger brothers. After their parents divorced, the three siblings lived with their mother, who was an extreme perfectionist (especially about schoolwork). Peniche attended a modeling class at age twelve. After briefly moving the family to Houston, Texas, Peniche's mother remarried and moved them to a home on Blue Lake in Fairview, Oregon. At age 16, Peniche won a six-week contract to model in Korea. She returned for another six-week stint at age 18.

Peniche attended Portland Lutheran High School in Gresham, Oregon, where she was a Cheerleader. She graduated in 2002, and later attended Portland State University and took classes through UCLA Extension. In a 2008 interview with Steppin' Out magazine, Peniche claimed that she was sexually abused as a minor, teenage model, and beauty queen; also physically abused by a former boyfriend.

Peniche won the Miss Oregon Teen USA 2002 title in November 2001. She competed in the Miss Teen USA 2002 pageant but did not place. At the end of her reign she crowned Tami Farrell as the new Miss Oregon Teen USA. The following year she represented Oregon in the Miss United States Teen pageant, which she won. She was crowned November 10, 2003 in Chapel Hill, North Carolina. Peniche was considered an unconventional pageant winner, for her fashion and career choices.

In September 2006 Aaron Carter, then 18 years old, proposed to Peniche while they were onstage in Las Vegas, Nevada. They had known each other five days. Peniche, who had previously dated his older brother Nick, agreed. The engagement was broken off six days later.

Starting in November 2009, Peniche appeared as a patient on the VH1 reality television spinoff series, Sex Rehab with Dr. Drew (a documentary about the treatment process for sexual addiction patients [filmed in April 2009] at the Pasadena Recovery Center). Peniche described herself as having had hundreds of lovers, but being unable to emotionally connect with anyone in any kind of relationship. Peniche's participation in the treatment program was marred by her aggressive and erratic behavior: verbally abusing the staff and other patients; refusing to participate in group discussions, or obey the clinic's rules; forcefully demanding that the staff fetch her fruit juice and bring it to her bedside; accusing people of laughing at her when they clearly were not; and, compulsively smiling (as a beauty pageant contestant might, in order to maintain a facade of well-being) -- even when discussing her own past traumas and pain. Dr. Drew Pinsky, the treating physician, became suspicious that she was using illicit substances such as methamphetamine, or had been prior to being admitted. The PRC's staff Psychiatrist diagnosed her as having borderline personality disorder (BPD). It was indicated that both the substance abuse and BPD had to be treated before any treatment for sexual addiction could begin. Eventually, Peniche was involuntarily discharged for failing to comply with the program's guidelines. She refused Pinsky's offer of an alternative program at a nearby psychiatric hospital, and during the process of being evicted from her home, she made suicidal gestures and became abusive toward the show's production staff (e.g., throwing a container of water onto a technician).

Peniche wed investment builder Justin Williams in February 2011 in Los Angeles, California and they have two children together, a son named Preston and a daughter named Layla. Their marriage has been strained, reportedly due to Peniche's behavior, both past and present; her husband has made allegations of infidelity against her and of child abuse, saying a hair follicle test showed she'd exposed their then 10-month-old son to methamphetamine.

Peniche joined the cast of Celebrity Rehab Presents Sober House, in which she transferred into a sober living facility (often an interim step between rehab, and returning to society). In the first episode, she became verbally abusive toward the sober living manager (Jennifer Gimenez), and tested positive for methamphetamine. During the second episode, admitted being worried that her former Rehab co-star, Mindy McCready (whom Peniche had invited to move in with her at the end of their season on Rehab—an idea that Dr. Pinsky openly opposed) had access to sensitive materials on Peniche's computer. (It was later reported that the two argued over money, and, an accusation over a stolen hard drive [containing the nude video featuring Peniche, Eric Dane, and Rebecca Gayheart]).) As Peniche was being filmed returning home to address this matter, she punched a cameraman in the eye, and was evicted from the sober living facility. A few days later, Head Counselor Bob Forrest brought Peniche back to the facility to see if the residents would accept her return; but, (with the exception of co-patient/-resident Tom Sizemore), the residents declined Peniche's in-person plea to return, and she left amid stinging criticism by Heidi Fleiss.