Olivia Newton-John's Daughter Chloe Lattanzi Releases New Song 'Phoenix' on Late Star's Birthday: 'I Promised Her' (Exclusive)

Chloe Lattanzi is keeping the promises she made to her mom Olivia Newton-John.

In honor of what would have been the Grease star's 76th birthday on Sept. 26, Lattanzi, 38, has released "Phoenix", an empowering new single that her mom, who died of breast cancer two years ago, had encouraged her to finish.

"I co-wrote the song 'Phoenix' for my mom as a promise to fly, to know my own worth and to make sure to love myself," Lattanzi tells PEOPLE exclusively. She's long been open about her struggles with mental health in the past as well as recently, while grappling with the loss of her mother.

"I had struggled with PTSD and multiple things of the mind," she says. "So this was my promise to be happy, healthy, and love myself. She said the most important thing to her more than anything in the world is that her child, me, shared her gifts with the world and was happy."

Lattanzi began working on the song years ago, when Newton-John was still alive. "She would listen to it every day and she would just be like, 'Come on baby, put it out, put it out,'" she recalls. "But then Mama took a downward turn and the most important thing to me is taking care of my mom."

She continues, "So I'm really excited to release this song in her honor. And for anyone who's struggling with issues of the body, the mind, or the spirit, I want it to be a reminder to them that they are incredibly more powerful than they could ever imagine. You are not what has happened to you, and you are not the illness that you have. You are eternal, bright light."

The song follows Lattanzi and Newton-John's previous duets "Window In the Wall" and "You Have to Believe (We Are Magic)", the latter of which rose to #1 on the Billboard Dance Chart. "I remember being like two years old walking around the house singing. She said she could play a song once and I'd have it memorized. It was just kind of in my blood."

Aside from music, Lattanzi is gearing up to honor her mother's greatest mission, by leading the annual Olivia's Walk For Wellness in Australia to raise funds for the Olivia Newton-John Cancer Wellness and Research Centre.

"I'm so looking forward to seeing everybody dancing and the joy on their faces," says Lattanzi of the walk on Oct. 6 in Melbourne. This year the event is themed after her mom's 1981 hit song "Physical".

These days, Lattanzi is feeling Newton-John's positive energy more and more.

"I feel really proud of myself because I didn't feel strong at all when she passed. I felt like an 80-year-old inside of a 30-something-year-old's body. But I was like, 'I love her so much. I can't let this go down the toilet," she says.

"I saw what my mom went through with cancer, and I'm like, 'I want this to f---ing stop'. With the wellness center, the goal is making that the standard of care, the mind-body connection. I have a dream of expanding on that."