Beth Nielsen Chapman Says Olivia Newton-John's 'Friendship' Helped Her Through Cancer Treatments

Olivia Newton-John not only used her journey with breast cancer for activism and education, but also as an inspiration to a friend in need.

Beth Nielsen Chapman — a songwriter who often co-wrote with longtime friend Newton-John, who died on Monday — is opening up about her own cancer journey, and how the Grease star helped her through it.

"In the year 2000, I was diagnosed with stage two breast cancer. I remember getting a phone call from Olivia on the day that I was diagnosed. I was a single mom ... and my son was about 19 going into college," Chapman, 63, tells PEOPLE of the day she was diagnosed, after her own husband had died of cancer in 1994. "I was just reeling and she called me up and she said, 'I'm gonna put you in touch with my oncologist, he's gonna call you.' She gave me his home phone number and she was right there — incredibly helpful."

She continues, "She knew that day that you're diagnosed; she knew that feeling. She understood the way the world just kind of goes all crazy. And you're just trying to think straight, know what to do next. It turned out to be incredibly helpful."

Imelda Michalczyk/Redferns Olivia Newton-John and Beth Nielson Chapman

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After speaking with the oncologist, Chapman says she was able to "calm down" and find her "center." Meanwhile, Newton-John served as an "incredible friend" and offered her sound advice.

Ray Tamarra/GC Images Beth Nielsen Chapman and Olivia Newton-John

"Olivia and I are talking on the phone, and she knew I was getting ready to go into some pretty heavy-duty treatments. She said, 'Beth, I really want you to think you've made a decision. And this is how you're going to treat this right. So be open to it and don't fight it, it's not a fight thing,'" she recounts. "So when I went in for my first treatments, instead of thinking of it as poison going into my veins, I literally put on a very relaxing tape of music. And I tried to go into a meditation and I imagined this beautiful blue light going through me, that was just cleansing out all of the cells I didn't need."

By the end of her treatments, Chapman considered the "Hopelessly Devoted to You" singer to be one of the reasons she made it through.

"I went into a full remission but I counted her friendship and her guidance as one of the main things that really helped me see that and we pass it forward," Neilsen Chapman tells PEOPLE. Paying it forward eventually led her to serve on the board of directors of an organization the star co-founded, called Healthy Child Healthy World.

"This is one of the many ways that Olivia worked to make it a better world. Everything she touched was enhanced by her presence and her determination to turn things around and she was always so incredibly positive," she adds. "I will never forget that that year and a half when I was going through treatment. I was able to pick up the phone and talk to her at any time and she was always so inspiring and so helpful. We stayed really close friends."

Chapman and Newton-John most recently got together with fellow songwriter Amy Sky to write an album titled Live On, which was released in 2016. "We created this whole album, around just songs to help people going through grief, which of all people, Olivia Newton-John knew about grief and how to keep your life moving forward," she says.

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Chapman says that beyond her cancer activism, Newton-John's creative work will live on for generations. "With all of the success of Grease, there's going to be 3-year-old, 5-year-old little girls falling in love with Sandy for the next 100 years. So timeless."

Newton-John died Monday at age 73, five years after announcing she had breast cancer that had metastasized to the sacrum. Her husband, John Easterling, announced her death on her social media channels, sharing that the star was surrounded by family and friends at her ranch in Southern California.

"Olivia has been a symbol of triumphs and hope for over 30 years sharing her journey with breast cancer," his statement read. "Her healing inspiration and pioneering experience with plant medicine continues with the Olivia Newton-John Foundation Fund, dedicated to researching plant medicine and cancer. In lieu of flowers, the family asks that any donations be made in her memory to the @onjfoundation."