Ladd replaced Fawcett and played her character's sister Kris Munroe for 90 episodes between 1977 and 1981.
But the actress was convinced she'd face a bitter backlash from Fawcett's loyal fans.
She says, "I was really nervous because I was stepping in and hoping beyond hope the show would work with me in it. Let's face it, there were big shoes to fill. So I said, 'OK, if I could be funny and make mistakes, then I have something to play that makes sense to me.'"
Ladd paid tribute to her predecessor at Saturday's (17Apr10) TV Land Awards, where Fawcett was honoured with a special tribute - 10 months after she lost her battle with anal cancer.
The untitled computer-animated film is in pre-production at Lucas' Skywalker Ranch production facility in Marin County, California, according to the Hollywood Reporter.
The musical marks a rare step outside the Star Wars universe for the filmmaker, who last directed Star Wars: Episode III - Revenge of the Sith in 2005.
Elf writer David Berenbaum wrote the screenplay, which is tightly under wraps but is rumoured to feature fairies.
Teenage Mutant Ninja Turtles' Kevin Munroe is directing the project, which is expected to feature songs from a variety of sources.
A Lucasfilm spokesperson says it is "too early to comment on the details of the project".