Priscilla is an executive producer of the film. It's claimed that she and Sofia approached Elvis Presley Enterprises (EPE) to ask about using Elvis' music in the movie, but were turned down. The company controls the late singer's $18 billion estate.
"This was a real kick in the teeth for her," our source says.
"It's going to be a challenge for viewers to immerse themselves in Elvis and Priscilla's love story, without his music."
EPE owns 85 percent of Elvis' estate and has full control over his music rights. Lisa Marie's eldest child Riley is responsible for the estate's remaining 15 percent, after inheriting it upon the star's death in January aged just 54.
Our source stresses that Riley, 34, was not responsible for turning down Priscilla's request, yet the rejection has still stung her still-grieving grandmother.
Being knocked back was also particularly galling for Priscilla who was divorced from Elvis at the time of his death on August 16, 1977, as EPE permitted the use of the King's original music in Baz Luhrmann's 2022 film Elvis.
After Riley was named the sole trustee of Lisa Marie's estate in June, it seemed the family drama was behind the pair.
"When my mum passed away there was a lot of chaos in every aspect of our lives," Riley told Vanity Fair in September.
"We are family, but there's also a huge business side to our family. So I think there was clarity that needed to be had."
As she and Priscilla move on, it's clear protecting her late grandfather is Riley's top priority.
"The Presley name is a legacy and they're nothing but temporary custodians of it," says our source.
"Riley knows she has to pass this down to [her twin half-sisters] Finley and Harper, and the next generation of Elvis' family."
"Despite the setback, insiders say Priscilla still hopes her movie will be a smash - even without Elvis' iconic tunes.