March 16, 2018 12:25 PM

Demi Lovato and her mom, Dianna De La Garza, are opening up about their shared experiences with mental health, disordered eating and substance abuse.

On Friday, De La Garza and the pop star stopped by Good Morning America to promote the matriarch’s new memoir Falling with Wings: A Mother’s Story, which was excerpted exclusively in PEOPLE earlier this month.

“I feel very proud of her,” Lovato, 25, told GMA’s Michael Strahan of her mother, who in her tell-all revealed her experiences with anorexia, depression, PTSD, domestic violence and Xanax addiction.

The “Sorry Not Sorry” singer has been vocal about her own struggles with bipolar disorder, self-harm, bulimia and substance abuse.

“I know it’s something that’s not easy, first-hand being somebody that’s struggled with mental illness and being open and talking about it: I know that it’s not easy to be open with the world,” Lovato said on GMA.

Dianna De La Garza and Demi Lovato
Courtesy Dianna De La Garza

“The changes that I’ve seen in my mom: She’s happier, and she’s calmer,” Lovato added. “She used to suffer with anxiety, and when she self-medicated, she was more depressed, and she kind of had a cloud over her. Now she glows, and she is just so cheerful, and she’s the most positive person I know.”

De La Garza, 55, revealed on the morning show that her daughter — who as of Thursday has been sober for six years — inspired her to seek treatment and write her book.

RELATED: Demi Lovato’s Mom Opens Up About Escaping Her Abusive First Marriage: ‘I Knew I Had to Get Out’

“Demi’s the one that gave me courage — because she was being so open and honest and vocal about her struggles, and I saw how much it was helping people everywhere,” De La Garza said. ” I thought, ‘I want to be honest and open and tell the whole story and I want to be a part of that.'”

In a previous interview with PEOPLE, De La Garza said she and her daughter work on their issues together.

Dianna De La Garza and Demi Lovato (2009)

RELATED: Demi Lovato’s Mom on Her Family’s Mental Health, Addiction Journey: What Do You Say When Your Child Is Paying the Bills?

“One of the biggest things they teach you in therapy is that you need a good support system. And so my becoming healthy was something that we could share, and we could support each other with,” De La Garza said at the time.

“To this day, if one of us is struggling, we can reach out to the other and say, ‘I’m having a hard time today, can you talk to me about it?’ And it is absolutely one of the most rewarding things about getting healthy, as a mother, and being able to help your children,” she added in the PEOPLE interview.

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