Lisa D'Amato (left) and Mindy McCready
Brian Ach/WireImage; Randi Radcliff
02/19/2013 at 01:00 PM EST
On Sunday night, when news hit of Mindy McCready's apparent suicide
, Lisa D'Amato got a phone call from actress Mackenzie Phillips, a cast mate on season 3 of Celebrity Rehab with Dr. Drew.
"We were just trying to put it all together, figure out what happened," D'Amato tells PEOPLE. "Mackenzie doesn't know either. The one thing about Mindy is that she was very much seeming to be fine and perfect on the surface, but she was battling a lot."
McCready, 37, became the third person from their season to die
, joining musician Mike Starr and reality star Joey Kovar. "I'm just numb," says D'Amato. "She was such a beautiful, warm-hearted, giving, lovely woman."
D'Amato stayed in contact with McCready off and on since the show. Their last exchange was about a year ago, when McCready sent a text message congratulating D'Amato on winning
the all-star edition of America's Next Top Model
in December 2011.
"She wanted me to come and visit her at her house," she says. "Her text message was: Finally you got what you deserved."
The cast members forged a deep and lasting bond.
"We went through therapy, and we know more about each other than people who have known us their entire lives. It's a very sacred private time," she says. "And now it feels like half my cast is dead. I am devastated."
And although a total of five Celebrity Rehab
cast members have died, D'Amato has only praise for Drew Pinksy.
"He's doing everything right. That's why so many do get saved," she says. "But it's up to the patient to continue with their sobriety or to continue with the efforts to have a better life. He can't live their lives for them. He gives you the tools and it's up to you to use the tools. Dr. Drew is amazing."