Kelly, one of the Beatles' longest-serving employees, worked for the British band for more than a decade but had never shared her stories publicly until now.
She breaks her silence in a new documentary, "Good Ol' Freda," which had its world premiere on Saturday on the second day of the South by Southwest Film Festival in Austin.
"It's such a classic Cinderella story: Girl picks the job of a lifetime," director Ryan White told Reuters.
The tale is sure to delight fans of the Beatles, but White seeks to tell a story that transcends that audience, a story about an amazing decade in an otherwise ordinary life.
The film features four Beatles songs, which required the permission of many people, including the two surviving Beatles. It also includes never-before-seen photos of the band.
The documentary's title comes from the Beatles' 1963 Christmas recording, in which George Harrison thanks their secretary in Liverpool, and they all yell, "Good Ol' Freda!"
A mutual friend and a family connection to the 1960s' Liverpool music scene brought Kelly to the attention of White, who took the opportunity to tell her story.
The Los Angeles filmmaker, 31, who co-directed and produced the 2010 soccer documentary "Pelada," grew up knowing Kelly as a family friend who was a secretary. In fact, she is still a secretary, for a Liverpool law firm.
"I didn't know that she had a crazy back story," White said, adding he only discovered it when a friend put them in touch two years ago.
Kelly, now in her late 60s, says in the film that she wanted to record her stories for her 2-year-old grandson - stories that in many cases she never got around to telling her family.
Kelly, described by White as shy and humble, insists in the documentary that no one would be interested in hearing her story.
'I WAS A FAN MYSELF'
The loyal secretary, who was 17 when she started working for the band, has no intention of dishing dirt about her former famous employers, so White focused instead on her compelling personal narrative and interactions with the Beatles.
Kelly arranged bookings, cut paychecks and stayed up all night responding to fan mail. At the height of Beatlemania, the band received 2,000 to 3,000 letters a day, she said.
The Beatles - Harrison, Paul McCartney, John Lennon and Ringo Starr - became the most famous pop band in history. They entered the Guinness Book of World Records in 2001 as the world's best-selling group, with more than 1 billion records sold.
"The amount of personal attention and true affection that she served the Beatles' fans with - teenage girls, mostly - will probably go unmatched throughout music history," White said.
Kelly was briefly fired by Lennon after she arrived late before a show because she had been having drinks with an opening band. The secretary convinced Lennon to get down on his knee and beg her to stay.
"Freda was like part of the family," Starr says in the film as the closing credits roll.
Kelly closed down the Beatles' fan club offices after the band broke up in 1970, taking with her boxes of autographs, photos and memorabilia. She did not sell them, instead giving them away to fans over the years, White said.
Kelly, who attended Saturday's premiere and answered questions from audience members, says in the film that she did anything she could for club members.
"I was one of them," Kelly says. "I was a fan myself."
(Editing by Peter Cooney)