In the film, based on the book of the same name, Aniston plays a Rosie Dickson, a former beauty pageant queen whose plus-sized daughter, Willowdean (played by Danielle Macdonald), signs up for a beauty contest amid a struggle with body-image and self-esteem.
Author Julie Murphy, who penned the novel, has said in the past that her story was inspired by some of Parton's songs. So, when Aniston decided to serve as a producer on the adaptation, one of her first calls was to the "9 to 5" songstress, asking her to be a part of the project.
"I got a call sayin' Jennifer Aniston had taken the book and was gonna make it into a movie," Parton explained in a sit-down interview for the special. "I said, 'I would love to do the music!'"
So Parton came on board to record some new renditions of her most beloved hits for the soundtrack -- as well as a few new tunes, including, "Push and Pull," which features Aniston singing backup vocals.
"I have to say, I got to know her [and] she's such a pro! So sweet," Parton shared, adding that her husband, Carl Dean, "absolutely loves" the Mother's Day actress.
"He was more excited just [about] me working with her then I was when I got the whole soundtrack [job]," Parton added with a laugh.
Parton's candid interview and recording sessions -- featuring some of her closest musical friends like Elle King and Miranda Lambert -- are part of the upcoming TV special Dolly & Friends: Making of a Soundtrack, which airs Thursday at 9 p.m. ET/PT on CMT.