For nearly five decades, little was known about Mary Jo Kopechne, the 28-year-old campaign worker for Robert F. Kennedy who tragically died when the Oldsmobile Delmont 88 driven by his younger brother, Ted, went off a small wooden bridge in Chappaquiddick on July 18, 1969 — and she was left trapped inside.

Chappaquiddick, a new movie opening April 6 that explores the events of that night and the week that followed — when Kennedy pleaded guilty to leaving the scene of an accident — has once again brought questions about what happened that evening to the forefront. Yet it has also brought attention to Mary Jo, whose story was long overlooked in the headlines that followed, which primarily focused on Kennedy and his thwarted political career.

“For 49 years people have wanted to know what happened,” Mary Jo’s aunt Georgetta Potoski, 75, says in an exclusive interview in this week’s PEOPLE. “Maybe now Mary Jo will be brought to the forefront and remembered not just for how she died but for who she was.”

Potoski and her son, William Nelson, 46, hope the film will convey something about the real Mary Jo, who was reduced at the time to what William calls “the quote-unquote ‘Girl in the Car.’ ”

Mary Jo, who worked for RFK for four years, was in Chappaquiddick, off Martha’s Vineyard, that weekend for a reunion party for her fellow campaign workers — known as the “Boiler Room Girls,” and nicknamed for the campaign office in which they worked.

For more on Mary Jo Kopechne’s life and tragic death, pick up the newest issue of PEOPLE, on newsstands Friday

“She was so much more than a secretary,” says Potoski, who is two years younger than Mary Jo and always thought of her as a sister.  “JFK’s idea of ‘ What you can do for your country,’ she really tried to do that. She was devoted to Bobby. She wrote up all his personal correspondence and typed up his declaration to run for President.”

Potoski also says “Mary Jo was devastated by his assassination.”

“[Mary Jo and her co-workers] loved him and they loved Ethel and the kids,” Potoski continues. “They believed they had a mission and it was catastrophic when he was killed because everything they believed in all of a sudden was gone. They didn’t have a leader anymore.”

Afterwards, she says Mary Jo “was trying to figure out what to do and how to process the brutality of what had happened to the Kennedy family. She and some of her co-workers were given the task of cleaning out his office. That was their last job for him.”

After her death, Mary Jo’s parents, Gwen and Joe Kopechne, were “crushed” by rumors about their daughter and Sen. Kennedy that followed the accident.

“There were all the innuendoes they were having an affair, or something salacious going on,” says Potoski, “but if you knew who she was, you’d know that didn’t happen. She was thinking of getting engaged, but no one came out to defend her, and her parents were broken — and they just retreated.”

She adds that Mary Jo “wasn’t particularly fond” of Ted Kennedy.

“They called him the office boy,” she says. “He was a young man finding his way around Washington, but he didn’t have the same focus that his brothers  had — at least not yet. He didn’t really impress her as picking up the standard for Bobby.”

Nearly fifty years later, Mary Jo’s remaining family hopes the world will learn about the young woman they loved. “She was charming, she was funny, she was a little uptight,” says Potoski with a smile. “If you knew a dirty joke, you didn’t tell it to Mary Jo.”

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She also remembers how her niece “loved to jitterbug and she loved the Brooklyn Dodgers, she was a bit of a tomboy.” She also relished her career in Washington.

“She really believed she could make a difference,” says Potoski,  who’s written a book with her son, Our Mary Jo, about her life. She also launched a scholarship in her name at Misericordia College, to be given out for the first time this year. “There is no doubt she would have done great things in her life.”

Meanwhile, Potoski’s son adds that “We’re happy more information is coming out — that’s the path to the truth.”