Her mother admitted she "can't really say for sure" what led to her daughter's relapse.
"I knew that she wasn't sober," De La Garza said of Lovato, who apologized for no longer being sober in her ballad "Sober," released in June. "I didn't know what she was doing because she doesn't live with me and she's 26."
De La Garza recounted the moment she found out about Lovato's overdose, saying that text messages alerted her that something had happened. "The one text message that clued me in on what was going on said, 'I just saw on TMZ and I'm so sorry,'" she said. "Before I could get to TMZ, I got the phone call from her assistant and she said, 'We're at the hospital.' So then I knew, OK, she's not gone. She's here. And I said, 'What's going on?' And the words that I heard are just a nightmare for any parent: 'Demi overdosed.'"
In August, Lovato shared an emotional message on social media about overcoming addiction: "I now need time to heal and focus on my sobriety and road to recovery," she wrote on Instagram. "The love you have all shown me will never be forgotten and I look forward to the day where I can say I came out on the other side. I will keep fighting."
Listen to the latest interview with her mom below.