[Note: This story contains plot revelations about the Sundance film “The Sentence.”]

PARK CITY, Utah — Cindy Shank remembers all those years in prison, trying to find a way to still be a mother to her three young daughters.

There was the time when, craving a Halloween experience with her children, she made costumes out of what was available — toilet paper — and took them trick-or-treating in the prison visitation area.

There were the visits when she found an empty room so she and the girls could have a spontaneous karaoke party and sing Taylor Swift songs together.

And there were those many years of weekly phone calls — 15 minutes total, five for each daughter — in which she would describe her cell to her daughters and listen to them tell of their bedrooms in the suburbs of Lansing, Mich. That was the strangest part — a bond tight enough to practically feel over a phone line but never being close enough that she could see their rooms or be in there with them.

“I remember Ava used to say, ‘My Mommy is a phone,’ ” Shank, a 45-year-old of Mexican American heritage, recalled, referring to her middle daughter, who was barely 2 when her mother was incarcerated.

“I would hold the phone tight,” Ava, now a 12-year-old of subtle-but-Instagrammable theatricality, said as she sat across from her mother. “While we were talking, I would wrap myself in a blanket she knitted for me so it was as if she was holding me.”

“She would say, ‘Mommy, you have your arms around me,’ ” Shank recalled.

“And then I’d hear the beep” signaling the end of the call, her daughter said.

Shank; her daughters; her ex-husband, Adam Shank; and her brother, Rudy Valdez, were eating dinner in a neighborhood restaurant in Park City on Saturday evening with about a dozen friends and relatives. A few hours earlier, they had attended the world premiere of the documentary “The Sentence,” watching as years of their lives unfolded on a screen to hundreds of strangers at the Sundance Film Festival.

Valdez had spent a decade shooting footage that would turn into “The Sentence,” documenting his nieces for his incarcerated sister in what began as a personal project but became something more ambitious.

The painfully intimate film depicting young girls coming to terms with their doting mother’s long-term absence prompted many tissue-pulls during the screening and a tear-streaked standing ovation when it ended. A question-and-answer session culminated in a line of total strangers coming to the front of the theater to hug Valdez, Cindy and Adam Shank, and the Shanks’ three daughters, Autumn, Ava and Annalis.

“You girls stuck together. You’re an inspiration,” one said as she hugged Annalis, 10. The girl gave a good-natured smile and, unsure of what else to say, offered a polite, “Thank you.”

“You have a great mom,” another said to Autumn, who is 14. She looked a little uncomfortable, then slipped away a moment later to retrieve a coat she’d forgotten at her seat.

Cindy Shank was prosecuted in 2007 on drug conspiracy charges after living in the late 1990s and early 2000s with a boyfriend who was a dealer. Although she said she had no involvement in his activities — and although he had died in a shooting six years earlier with no charges filed against Shank — law enforcement authorities had a change of heart. They revived the charges and arrested her early one morning in her home with her daughters sleeping inside. Because they were drug charges, the subsequent trial resulted in a 15-year mandatory-minimum sentence in a federal prison.

“The Sentence,” which is seeking a distribution deal at Sundance, is poised to do for unjust sentencing what “An Inconvenient Truth” did for climate change. If Al Gore was the hero Americans at Sundance and beyond needed in 2005 — a welcoming, professorial face to associate with the fight against environmental catastrophe — Shank and her daughters offer the criminal justice equivalent, giving a human access point to what many experts describe as a sociological disaster.

Shank spent nearly nine years in prison before a rare clemency exception, pursued doggedly by Valdez and Adam Shank, was granted as President Barack Obama prepared to exit office in late 2016.

Although she got out of prison just 13 months ago, Cindy Shank, who now works as an administrative assistant in Michigan, has the kind of irrepressible spirit that would stir envy in the sunniest Midwestern soccer mom.

“Remember the time we binge-watched all those episodes of ‘Gilmore Girls’?” she said to enthusiastic nodding from Annalis. “I loved the relationship between the mother and daughter. Maybe because she’s such a cool mom.”

Shank served much of her term at the Federal Correctional Institution in Pekin, Ill., and later was at another federal facility in the Orlando area. When other kids would get on a flight bound for Disneyland over Christmas vacation, Autumn, Ava and Annalis would sit on the plane, telling flummoxed flight attendants cheerfully asking why they were going to Orlando that they “were going to see their mom.”

At dinner in Park City, Autumn, who has a quiet sadness, gave her mother a rare grin.

“So was it like ‘Orange Is The New Black’ ”?

“I never saw the show. I lived the show,” Shank said, laughing.

Shank doesn’t describe in great detail what it was like in prison. Mostly she offers that she “wasn’t making license plates.” (She performed a variety of jobs as part of the federal Unicor program and also took, and eventually taught, legal classes.)

She stayed in close touch with her brother, 38, who while he was shooting the movie was also making repeated trips to Washington to lobby organizations on his sister’s behalf and on behalf of the millions of Americans who have been incarcerated under mandatory-minimum laws.

“The farther you get in, the more cynical you become. I don’t know how anyone in this country can get a fair shake,” Valdez said, describing a prosecution against Shank that became a “numbers game” as attorneys sought an 89-year prison sentence despite the nonviolent nature of the charges. “Someone asked me, when I was meeting with activists, to tell them in one sentence why my sister went to prison. And I said, ‘She went to prison because we’re poor.’ ”

Mandatory-minimum laws, devised and strengthened over much of the second-half of the 20th century for drug and other offenders, have begun to be relaxed in recent years. Victims-rights advocates have argued that they punish nonviolent offenders and their families for no discernible judicial or rehabilitative reason.

“You never get an apology when they tell you you’re being granted clemency,” Valdez said. “You get, ‘Now, don’t screw up.’ ”

Valdez hopes his work will serve as a reminder that, for all the abstractions of criminal policy, many of the millions of people who sit in prison for years are not hardened criminals and loners but mothers and fathers in ordinary families simply struggling to get by.

Adam Shank, a burly, red-haired man who speaks softly, went about his job as a plumber and construction worker after his wife went to prison, often working two jobs even as he functioned as a single dad. The events took their toll on his marriage to Cindy, but the two would find a way to co-parent when she was behind bars and continue to do so now, with the children splitting their time between their two houses.

“There were always a lot of adjustments, but we’ve just tried to figure out a way to keep things as normal as possible,” Adam said.

“I don’t want to hide what I went through from my children, but I don’t want to put any of it on them, either,” said Cindy, who played down any idea that she suffered trauma as a result of so many years in prison. “But it’s a difficult balance.”

Nearly all of the women Shank met behind bars were mothers. Some were on the phone every night trying to find a place for their children to sleep. Many had been behind bars for years.

“You’d hear people complain about 15 days, and I’d think, ‘If you only knew,’ ” she recalled. “But I also had to remember not to say anything about my own [15-year] sentence. Because there were people there serving 30 years on nonviolent charges because they were related to crack. So you never say anything, because someone always has it worse than you.”

Before the screening, Annalis was taken by all the people filing into the theater.

“So are we watching every Sundance movie or just ours?” she asked, sitting in the same row as her father and sisters toward the front of the theater.

A moment later, she noticed the still image of her family on the movie screen touting the upcoming film. “That’s me as a baby,” she said.

“You were a month old when Mommy went in,” Adam Shank told her. “Mommy was supposed to go in earlier, but we worked out the sentencing to get a delay so you could be born outside.”

Annalis grew quiet as her eyes registered this information.

In the green room after the screening, the comic actor Craig Robinson entered, awaiting the screening of his film. He sat down on a  couch and began singing a dramatic rendition of an Elton John song to no one in particular.

Cindy Shank eyed him with amusement. She decided to walk up and take a selfie, even though she was not sure who he was.

After Robinson told her of his fame, she fixed him with a stare and then said, “I’m a superstar, too. I’m prison-famous,” before bursting out laughing.

“We watched a lot of TV inside,” she said after leaving the green room. “But I couldn’t remember what he was from,” she said with a shrug.

In the year since she was released, Cindy Shank and her daughters have been engaging in as many activities as possible — kayaking, drive-in movie theaters, bicycling to the zoo. That the zoo was flooded only added to the adventure.

“There was that snake,” Ava said.

“Yes, the snake. It was still fun, though,” Cindy said.

Annalis pondered that. “I didn’t like the snake.”

Cindy looked at her children with her eyes glistening. “I missed a lot of the early parts,” she said. “Annalis learning to walk or Ava learning to talk. But I’ll get a lot of other stuff — prom and weddings and grandbabies.”

She took a deep breath, then spoke again. “I’m not trying to make up any time. That’s all gone. I’m just trying to live where we are now.”