Demi Lovato's mum struggled to approach her daughter about her past bad behaviour because the singer was paying "most of the bills".

Demi went through rehab when her substance abuse and body image issues led to a meltdown on tour with the Jonas Brothers in 2010, and now her mum, Dianna De La Garza, has opened up about those troubled times in her new book Falling with Wings: A Mother's Story.

She claims she started to notice her daughter's problems in 2003.

"One day (Demi's sister) Dallas came running into the dining room looking alarmed," she writes in her memoir. "(She said), 'Demi is visiting some really weird websites about anorexia and bulimia'. I sighed (and said), '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."

By the age of 16, Demi was ignoring her curfew and her mother suspected she was getting into drugs and alcohol, but she didn't know how to confront her about it.

"Every night I'd set an alarm for 2am. If she wasn't (home), I called her until she walked through the front door," she continues. "What do you say to your child when she is the one paying most of the bills?"

However, Dianna knew it was time to seek out treatment after the incident in 2010, when Demi attacked a dancer, and she admits she was shocked when she finally discovered what her daughter was going through.

"As the intake counselor asked questions, I heard more than a few shocking revelations," she writes. "When she asked about drugs, my jaw dropped: 'Cocaine, pot, and Adderall,' Demi said. My blood ran cold."

Demi has now been sober for over five years and she has been very vocal about her mental health struggles.

She admits she is proud of her mum for being open about what she was going through as a parent.

"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, tells "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."