Allemand, a star on "The Bachelor," hanged herself with a vacuum cord in her New Orleans home.
Donna Micheletti, Allemand's mother, was on the phone with the 29-year-old when the phone went silent -- when Micheletti thinks Allemand committed suicide. On "Dr. Phil," Micheletti told McGraw that she was "destroyed" by Allemand's death.
"I'm the closest person in the world to her, and she didn't want to be alone when she left this world," Micheletti said.
"So she wanted Mommy to be there, I guess … It destroys me, but if it made her feel better, then that's fine. I don't mind dealing with this."
"I heard her last breath," Micheletti said.
Allemand's body was found by her boyfriend, NBA player Ryan Anderson, on Aug. 14. Anderson arrived 20 minutes after receiving a worried message from Micheletti, and found her unconscious.
She was rushed to the hospital and put on life support, but died two days later after doctors determined she suffered a "critical loss of brain and organ function."
The full interview airs Tuesday on "Dr. Phil."