Five years ago, Kathy Dillaber arrived at Ford's Theatre to see "Come From Away," Irene Sankoff and David Hein's musical set in the aftermath of 9/11, with arms crossed and a head full of skepticism.

As a former Department of Army civilian employee, now retired from the Pentagon — where she lost her sister on Sept. 11, 2001, and nearly died herself — Dillaber had no interest in seeing her trauma trivialized. Asked to guide the "Come From Away" cast and crew on a Pentagon Memorial tour, the volunteer docent did so through gritted teeth. Reluctantly, Dillaber also helped Ford's Theatre invite fellow Pentagon survivors to the preview performance of the new musical.

"Then the show began, I started to sit up and had an unexpected reaction," Dillaber says. "It was almost overwhelming but not — just the right antidote to soothe our mourning souls."

Based on a true story, "Come From Away" shines a light on Gander, the quaint Newfoundland town that welcomed some 7,000 stranded travelers when American airspace closed on 9/11. Heart-wrenching and heartwarming, with a propulsive folk-rock score, the show followed its 2016 run at Ford's Theatre with a move to Broadway the following year. Seven Tony nominations followed, as did the launch of a North American tour and extended productions in Toronto, London and Melbourne.

Along the way, Dillaber says she has seen "Come From Away" a dozen times at six venues, including a 2016 performance in Gander. She planned to add to that total Friday, when "Come From Away" commemorates the 20th anniversary of 9/11 with a free concert performance of the entire show, presented by Ford's Theatre, on the steps of the Lincoln Memorial.

"It's like watching 'It's a Wonderful Life,'" Dillaber says. "You still watch it every Christmas, even though you know the story line. ('Come From Away') is just a feel-good show, and a feel-good show that's not sappy. Everybody can relate to it — not to 9/11 but to loss."

Dillaber and Patty Mickley, her younger sister, were both working at the Pentagon when American Airlines Flight 77 leveled the building. Knocked to the ground by the impact, Dillaber escaped amid the debris. But she never saw her sister again. Mickley, who left behind a husband and a daughter who had just started kindergarten, was 41.

"I'm not anybody important," Dillaber says. "I'm just Patty's sister, and that's all."

Fifteen years later, Dillaber put on a brave face as she shepherded Sankoff, Hein and the "Come From Away" team through the same Pentagon courtyard where she saw her sister for the last time, minutes before the building was struck. Even as a theater buff — she's a volunteer teacher at the Little Theatre of Alexandria, Va. — she wanted nothing to do with the show itself.

"Thinking of it in retrospect," Sankoff recalls, "she was kind of patiently putting up with people who were turning the most horrific day of her life into a musical."

By inviting Dillaber and other members of the 9/11 community to that first preview, Sankoff and Hein — who penned the show's book, music and lyrics — sought to ensure "Come From Away" was being told with sensitivity. Just as they wanted to do justice to the hospitable residents of Gander and the "plane people" who found refuge in the town, the husband-and-wife duo wanted the show to honor those directly affected by 9/11.

"In writing it, we were trying to be careful about the words we use," Hein says. "So we use the words 'World Trade Center' once. We use 'the Pentagon' once. We use 'terrorist' once — only as necessary. Because of that, it has become a story that could be a response to almost any tragedy."

After attending the preview performance, Dillaber received countless emails from the survivors she invited, saying the show imbued them with catharsis and connection. Discussing the characters onstage, and the real people they were based on, Dillaber says, "They caught our attention, taking us away from the heartbreaking memories of 9/11." Her voice quivering, she pauses and gathers herself, then finishes the thought. "Taking us away, they made us smile and relax."

Dillaber has since gotten to know several of the people depicted in the show, including Kevin Tuerff, a marketing executive who was returning stateside from a Paris vacation with his boyfriend when their flight was grounded in Gander. Inspired by the kindness he met there, Tuerff began a tradition of closing his Austin agency every Sept. 11 and giving his employees $100 bills to do random acts of kindness — a gesture still carried on by his charity, Pay It Forward 9/11.

"Because of the show, I have now met many people who are either survivors from the World Trade Center or family members who've lost a loved one," says Tuerff, who befriended Dillaber after she took him on a Pentagon Memorial tour. "What they all say is that the show and the story of Gander doesn't change the terrible events of that day, but it provides a little bit of hope for humanity."

Sankoff and Hein say they also heard from a New York City Fire Department chaplain, who explained that "Come From Away" helped shift her memories of 9/11 from the pain of the day to the heroism that responded. Another woman, who lost a relative in the terrorist attacks, reached out to say that the show prompted her family to openly discuss that tragedy for the first time, after years of suppressing the topic.

Going forward, "Come From Away's" uplifting message will be more accessible than ever: On the same day as the Lincoln Memorial performance, a filmed version of the musical — shot this past spring at New York's Gerald Schoenfeld Theatre — started streaming on Apple TV Plus.

"The show provides us with a display of the best side of humanity in the worst of times," Dillaber says. "Every time I go to that show and the music starts, I just sit up and I am feeling good."

Did you know?

"Come From Away" was developed at Goodspeed Musicals' 2013 Festival of New Musicals in East Haddam. Old Lyme resident Sue Frost is founding partner of Junkyard Dog Productions, which is the lead producing entity of "Come From Away."