From PEOPLE Magazine Click to enlarge
The flight from Colombia to Peru on Oct. 28 was an especially turbulent one for Demi Lovato. As the singer-actress boarded the private jet she shared with the Jonas Brothers and their crew for the next stop on their world tour, Lovato was fuming: Tour managers had confronted her about partying with pals after hours, and she was convinced one female dancer had snitched. "Demi walked onto the plane, did not look at the girl, then suddenly punched her in the face and threatened her with a slew of expletives," says a tour member who witnessed the assault. Then, as Lovato walked toward her seat, four bodyguards positioned themselves behind her to head off any other possible outbursts while Kevin, Joe and Nick Jonas comforted the dancer. Eventually, one of Lovato's managers approached the star. " 'Are you in control at all?' he asked," according to the source. "She said, 'Sorry, I just lost it.' "

As the magnitude of her recent behavior sunk in, "Demi felt awful," says a source close to the Lovato family, "and she realized she needed to take personal responsibility for it." Hours later Lovato, 18, left the tour and-with her mom, Dianna, 48, and her stepfather-comanager, Eddie De La Garza, 45, by her side-headed to a treatment center to deal with what her rep called "emotional and physical issues." A source close to the family says her problems include longtime battles with eating disorders and cutting, a form of self-harm. "Demi is focusing on getting better," says the family source.

The shocking crisis comes as Lovato is at the top of her professional game: She has starred in three hit Disney Channel movies (the Camp Rock series and Princess Protection Program), headlines her own Disney sitcom, Sonny with a Chance (currently on hiatus), and has a burgeoning music career that includes touring and writing songs for her albums. But it's in part her fast rise that has led to her downward spiral. "She had Hollywood Records pushing her one way, Disney Channel pushing her another, and nobody allowed her a chance to breathe," says a source, who noticed Lovato's demeanor change after a 2007 move from Texas to L.A., where she lives with her parents and sisters Dallas, 22, and Madison, 8 (who currently costars in Desperate Housewives). "She is a girl who is overextended, and she couldn't handle it. She had a spark of exuberance in her eye that isn't there anymore."

The last six months haven't been easy. In May Lovato went through a heartbreaking split with Joe Jonas, 21, who has since moved on to a well-publicized romance with Twilight's rising star Ashley Greene, 23. "She was a true teenager in love," the source says about Lovato, who started dating Joe after they filmed Camp Rock 2 last fall. After only a few months together, Joe decided to end the relationship because "Demi's attitude and behavior were out of control," says a tour member close to Joe. Post breakup, "Demi was a mess and very angry," a Lovato insider says. (Soon after, she was linked to Wilmer Valderrama, 30; despite reports they're now a couple, his rep says, "They're not dating. He's being supportive of his friend during this difficult time.")

Her breakdown is about more than a bad breakup. One insider calls Lovato "tortured. This is a fragile girl who's experienced some serious issues long before she became a performer." Fame, however, fueled her problems. When Lovato first entered the spotlight, sources who worked with the star say she became more self-conscious about her body, refusing to wear short-sleeve shirts that showed her arms. Lovato-who has talked about how bullying has affected her self-esteem in the past-even tattooed "You make me beautiful" on her rib cage. The phrase, she says, refers to God and helps her "when I do look in the mirror and feel like I'm heavy," she told PEOPLE in August.

There were other visible signs she had troubling issues: In 2008-and again in 2009-photos of Lovato revealed red marks on her wrists, apparent signs that she had been hurting herself. "It wasn't a secret. She was getting help," says a source, adding that Lovato also has a life coach. Why didn't her parents simply insist their daughter take a break? One Lovato insider says: "They were not equipped with how to deal with someone going through a turbulent time. They're at a point where they're turning to experts saying we need help." In the past Lovato has often been difficult to work with. "I've seen her give one word answers to people trying to get information from her. She puts up a shield," says a Lovato insider. "It's not been easy."

The same could be said for what lies ahead for the teen. After the airplane altercation, "Demi knows she needs the help and knows that she is where she needs to be right now," says a family source. "Demi recognizes that she has a difficult road ahead." But can she come out of this a better person? "I have faith in her," says the Lovato insider. "It's not about Hollywood, a show or a recording career. This is about a girl being safe and growing up to be a happy adult."

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  • Reported by Sharon Cotliar/New York City.