"I felt my heart literally open up for the first time and like wrap itself around her. It was profound," Applegate tells PEOPLE. "And I'm more in love with her every minute of the day."
The magazine focuses on Applegate's new life after recovering from breast cancer, and becoming a mother to Sadie Grace.
"Yeah, now I'm Mom. She's healed me in so many ways," says the actress. "She's just made my life so much better. She's opened my whole soul."
People is on newsstands Friday.