Dianna De La Garza, Demi Lovato's Mom, Details Her Family's Mental Health and Addiction Journey

In a heart-wrenching new memoir, Dianna De La Garza, mother of Demi Lovato, opens up about her family’s battles with mental illness and addiction — and her famous daughter’s tortured path to success.

“I wanted to share this story because I thought there might be people out there who might be going through some of the same things that my family was going through,” Dianna, 55, tells PEOPLE of her book Falling with Wings: A Mother’s Story (with Vickie McIntyre). “It might help them in some ways.”

Over the years, Demi, now 25, has been open about her struggles with bipolar disorder, bulimia and substance abuse. Now for the first time, Dianna — in an exclusive excerpt in the new issue of PEOPLE — reveals her own journey to recovery from anorexia, depression and Xanax addiction.

“I’m so proud of my mom for achieving something she’s always wanted to do — tell her story,” Lovato, who wrote the book’s foreword, told PEOPLE. “She’s resilient, inspiring and strong. Because of her journey and strength to overcome the obstacles that she’s faced in her life, she is my hero.”

From Dreams of Stardom to an Abusive Marriage

Born Dianna Hart to strict Christian parents, she was raised in Irving, Texas, and developed a love for performing in church. After graduating high school, Dianna spent a season working as a Dallas Cowboys cheerleader before pursuing a career in country music. In 1984, she met and quickly married Patrick Lovato, who would become her manager. But their whirlwind romance soon devolved into a volatile, drug-fueled relationship.

Dianna says Pat, an addict whom she suspects lived undiagnosed with bipolar disorder, became violent. The couple welcomed two daughters — Dallas, in 1988, and Demetria “Demi” Devonne, in 1992 — and after 10 years of marriage, Dianna gave up her dreams of stardom and walked away from the marriage, summoning the courage to divorce him in 1994.

“I thought I could change him, and I think victims of domestic abuse often feel the same way. You’re not always going to be able to change someone, no matter how much you want to. There may come a point where your love for that person may not be enough to keep you safe,” says Dianna, who turned to a local women’s shelter when she decided to leave Pat. “I would ask them questions like, ‘Am I doing the right thing by splitting up my family?'”

Adds Dianna: “I didn’t feel like we were safe anymore. I knew I had to get out.”

As she writes in her book: “It broke my heart to realize that my girls had seen and heard so many things that must have terrified them. Starting over as a single mom was hard. But I finally felt free.”

Pat Lovato died of cancer in 2013, and Dianna says her daughters had a complicated relationship with him until then.

“Pat had a good heart. He really did. He loved his family; it’s just that he had mental health issues that were never addressed. And I think he covered up those issues with drugs and alcohol,” she says. “I always encouraged my girls to have a relationship with him… as long as he was responsible and wasn’t putting them in any danger. I wanted them to love him. They talked to him on the phone and tried to have a relationship with him, until he passed away.”

A Fresh Start — and a Barney Breakout

Dianna married Eddie De La Garza in 1995. As her daughters grew, she was delighted to see that they shared her love of performing; she entered them in pageants and talent shows. Then, just before Demi’s 9th birthday, she auditioned for and nabbed a role on Barney and Friends, where they met family friend Selena Gomez.

Dallas and Demi began to find mild success in entertainment. But Dianna — who welcomed her third daughter, future Desperate Housewives actress Madison, in 2001 — secretly dealt with depression and anxiety. But Dianna hoped her family’s Hollywood dreams would ease her struggles.

“My girls wanted to be stars, [and] the formula in my head looked something like this: stardom=money & recognition=less anxiety & more satisfaction=less depression & more happiness=fairy-tale life,” she writes in Falling with Wings.

Inner Demons, an Eating Disorder and Disney

After Demi’s stint on Barney wrapped in 2003, Dianna had her reenter public school, where she was bullied for her looks and acting career.

“One day Dallas came running into the dining room looking alarmed. ‘Demi is visiting some really weird websites about anorexia and bulimia,'” Dianna recalls in her memoir. “I sighed. ‘She probably got on them by mistake.’ I’m horrified when I look back. Sometimes we so desperately want to believe the best about our children that we ignore the obvious.”

Dianna reveals she missed similar warning signs when in 2007, Demi scored the starring role opposite Jonas Brothers Nick, Joe and Kevin Jonas in the Disney Channel original movie Camp Rock, then later her own show, Sonny with a Chance.

“[Years later] I found Demi’s diary,” Dianna writes in Falling with Wings. “One sentence in particular crushed my heart: ‘Nobody loves a fat rock star. Guess I’ll have to starve myself so people will like me.”

By the time Demi turned 16, Dianna lost control of her middle daughter, who was disobeying curfew and, she suspected, getting into drugs and alcohol.

“Every night I’d set an alarm for 2:00 a.m. If she wasn’t [home], I called her until she walked through the front door,” Dianna recalls in her book. “What do you say to your child when she is the one paying most of the bills?”

For much more on Demi Lovato’s mom, Dianna De La Garza — including an exclusive excerpt of her new book — pick up the latest issue of PEOPLE, on newsstands everywhere Friday.

Mother and Daughter Hit Rock Bottom

In 2010, Dallas quietly entered treatment for substance abuse. Then, in the fall, Demi made headlines while on tour with the Jonas Brothers when she punched a backup dancer in the face.

“That was the defining moment where we all said, as a family: ‘She needs help. She needs serious help. And it doesn’t matter what happens to her career — we need to focus on getting her the help she needs,'” says Dianna.

Dianna and Eddie begged her to get help.

“‘Maybe everyone would be better off if I wasn’t here anymore,’ she sighed, alarming us. In that moment, I didn’t see an 18-year-old young woman clinging to her career; I saw a child who was exhausted and afraid,” Dianna remembers in Falling with Wings. Demi checked into a residential treatment center outside Chicago. “As the intake counselor asked questions, I heard more than a few shocking revelations. When she asked about drugs, my jaw dropped. ‘Cocaine, pot, and Adderall,’ Demi said. My blood ran cold.”

Demi was treated for bipolar disorder, bulimia, self-harm and substance abuse at the treatment facility for three months. Shortly after, in 2011, Dianna’s battle with her own inner demons came to a head.

“I just had this breakdown,” says Dianna, who notes she struggled with anorexia since childhood, battled PTSD from her first marriage, had become addicted to Xanax and felt weighed down by depression and suicidal thoughts. “My girls came to me and said, ‘Mom, we’ve gotten help, and we’re doing good — now it’s your turn,” says Dianna, who entered the same treatment center that had helped Demi. “They did this intervention with me, they packed my bags for me, and they bought my ticket. Those things combined really were what set our family on the path to becoming mentally healthy.”

Upon reflection, Dianna regrets not recognizing her daughters’ issues earlier because her own struggles blinded her.

“I did not realize the extent and the danger of the mental health issues that they had,” she says. “I don’t like the word blame — blame, to me, says ‘I knew what I was doing, but I did it anyway.’ I believe in my heart that if I had known how dangerous the things they were going through at the time actually were, and if I had known then what I know now about mental health issues, I could have done more. I could have done things differently. I feel bad that they were going through things during a time in my life I didn’t realize my own struggles.”

One Last Intervention — and a Family’s Mission to Help Others

As Dianna worked on her recovery after her release, it became clear Demi had relapsed. Dianna, Eddie and more loved ones staged a “come-to-Jesus moment” for her in which Dianna told Demi she could no longer see her younger sister Madison as long as she was using; Demi acquiesced.

“That’s when she took her phone, smashed it and put it in a glass of water, as a sign that she was ready to commit,” says Dianna. “She gave up her phone, her car keys, her credit cards, she entered a sober living house and completely followed the program.”

Adds Dianna: “She’s never looked back.”

Indeed, after spending 12 months in a Santa Monica sober living facility, Demi is more than five years sober today. A Grammy-nominated vocalist, the “Sorry Not Sorry” singer is offering free counseling sessions from the treatment facility Cast Centers, which she co-owns with personal development coach Mike Bayer, on her Tell Me You Love Me World Tour.

Dianna hopes others struggling will seek solace in her family’s story.

“I used to think that her thing in life was going to be young girls looking up to her because she’s such a great singer,” Dianna says of her middle child. “But her purpose is so much bigger. I’m proud Demi is an advocate for mental health and positive body image — she’s a role model because of what she’s been through and where she is today.”

Falling with Wings: A Mother’s Story, by Dianna De La Garza (with Vickie McIntyre), is available everywhere March 6.