‘I do stupid things when I’m drunk,” says the heroine of Waitress. “Like sleep with my husband.” When the Broadway musical opens in the West End this month, it will represent the latest triumph for a project that began life 13 years ago as an inauspicious low-budget indie film. Set in a folksy small town in the American south, it tells the story of Jenna, a young woman who finds she now has an unwanted pregnancy to go with her unhappy marriage.

At least she has her waitressing job at Joe’s Pie Diner – and her burgeoning affair with her obstetrician – to keep her buoyant, not to mention the pies she bakes, each one named in honour of her state of mind, such as the Baby Screaming Its Head Off in the Middle of the Night and Ruinin’ My Life Pie.

This tart, stylised fable was the brainchild of the late actor-writer-director Adrienne Shelly, who made her name playing intelligent, beguilingly deadpan young women in The Unbelievable Truth and Trust, two arch comedies directed by Hal Hartley in the early 90s. First impressions count and Shelly’s opening scene in The Unbelievable Truth is a doozy: she lies in bed beneath a giant painting of a dollar bill and a photograph of a mushroom cloud, then sits up, stretches and yawns – while we hear the sound of a bomb exploding on the soundtrack.

Life of pies … Cheryl Hines, Keri Russell and Adrienne Shelly in Waitress. Photograph: Night And Day/Kobal/Rex/Shutterstock

The audience sees this beautiful, languid woman, a pixieish dead ringer for Rosanna Arquette. Yet what they hear is the sound of destruction. It’s a joke on the idea of a sex bomb, as well as a taste of what was to come from Shelly, who dedicated her career to exploding myths and stereotypes, as well as throwing light on neglected female experience.

Shelly’s life was cut cruelly short in November 2006. At the age of 40, she was murdered in her New York office by a construction worker, who tried to make her death look like suicide. She died not knowing that Waitress, her third movie as a director, had been accepted into the Sundance film festival after being rejected elsewhere. From there, it snowballed.

It is not the only thing that has endured. Shelly’s body of work and her tenacious methods are still inspiring film-makers and actors. Ally Sheedy, star of The Breakfast Club and High Art, is among them. “When you met Adrienne, she was this tiny, extremely beautiful little spirit of a person,” she says. “Then, as you worked with her, you saw she had this ferocious quality. She was not afraid, would not be intimidated, would keep creating no matter what. She was not going to wait around for agents to call, or for Hollywood to give her the parts she wanted. She was going to put on her running shoes and get out there and tell the stories herself.”

A day at gunpoint … Ally Sheedy in I’ll Take you There, written and directed by Shelly. Photograph: Two Left Shoes films

One such story is the prickly 1999 comedy I’ll Take You There, her second film as director. Sheedy plays Bernice, a crazed romantic who forces the dope who broke her heart to spend the day with her at gunpoint. At a time when US indie cinema was dominated by boys running around with firearms (Quentin Tarantino, Robert Rodriguez), Shelly flipped the gender roles, making the male character passive while giving the woman all the power.

“As far as I’m concerned, I’m basically playing Adrienne,” laughs Sheedy. “All that humour and craziness, the obsessiveness, the wild, colourful streak. I’d seen her in Hal’s films and loved her. I was amazed there was this young woman making films herself because there were so few women directing. She had motivation, drive, fearlessness. And she would do this thing of balancing absolute courage with a sense of feeling pathetic. She was a brilliant, sensitive, wounded heart. But in writing Bernice, she was laughing at her own hopeless romanticism, her absolute conviction that she was going to turn it all around and make it work.”

Auteurs are traditionally confined to the director’s chair, but Shelly was unusual in that her distinctive voice carried over into her acting, writing and film-making. “You could always see Adrienne poking through,” says Michael Roiff, who produced Waitress. “On set, she knew what she wanted. People who have an exacting vision can be brutal but she matched hers with a kindness.”

Sugary facade … the Broadway production of Waitress. Photograph: Joan Marcus

Waitress, which starred Keri Russell as Jenna, is shot in succulent fairytale colours and peppered with heightened, screwball-style dialogue, but Shelly insisted that the pain in the film should be real. That included Jenna’s ambivalence about her pregnancy. “I loved that,” says Cheryl Hines, who played one of Jenna’s waitressing colleagues, though she’s best known as Larry David’s wife in Curb Your Enthusiasm. “It’s pretty common for women to experience anxiety about having a baby but it doesn’t usually show up in movies. It’s hard to admit that you’re uncertain or scared. But I’d just had a baby and I did not love being pregnant, so I really responded to it.”

It’s also important that, in among the glossy pies, picket fences and Americana, the abuse dished out by Jenna’s husband is strongly felt: it hurts, especially the slap that comes halfway through the film, cracking its sugary facade. “People who didn’t like Waitress felt that tonally it moved around too much,” Roiff recalls. “But that was entirely by design. Adrienne said that real life is not compartmentalised. You don’t get to have your funny day and your sad day. It’s all mixed up. She ignored the rules and captured that feeling.”

This was already apparent in her 1996 directorial debut, Sudden Manhattan, a gently deranged comic thriller about a disillusioned New Yorker played by Shelly herself. While the heroine of The Unbelievable Truth was hearing bombs, Shelly has this character detecting an ominous rumbling in her breakfast omelette. Later, she witnesses two murders, only to encounter nothing but apathy when she tries to report them.

She was interested in making the sex scenes as awkward as possible Tim Guinee

Tim Guinee plays Shelly’s love interest, never quite able to consummate their relationship: a comic refrain is provided by shots of the couple lying in bed, fully clothed, after yet another abortive attempt at intimacy. “It was great doing those scenes with Adrienne,” Guinee says. “She was interested in making them as awkward as possible, which is completely the opposite of what everybody does with sex in movies.”

Each of Shelly’s films was shot quickly on a tight budget, with Sudden Manhattan tighter than most. “We had so little money,” says Guinee. “I was holding the boom pole when I wasn’t on camera, and I did some construction work, too. Adrienne was diminutive but she got exactly what she needed out of everybody, usually by being smarter and funnier. I really dug her. And she was terribly important for a lot of female directors. She was powerful on the scene in New York. I don’t mean she strutted around with that power – just that her actions were meaningful to people. She was breaking new ground, saying to women, ‘You do not have to fit the mould.’”

Roiff still finds it upsetting that Shelly didn’t live to see the effect Waitress had on audiences, starting with its premiere at Sundance in 2007, two months after her death. “I’ll never forget that,” he says. “The electricity, the anticipation, the brutal sadness in there – and then the uproarious response. Well, it goes back to what she said about the film: you don’t get to separate what’s sad from what’s not.”

Beguilingly deadpan … Shelly with Martin Donovan in Hal Hartley’s Trust. Photograph: Alamy

Hines also has vivid memories of that night. “I was sitting next to Keri and we were so overwhelmed by the honesty and the charm of it,” she says. “It’s one of those movies that people keep inside them once they’ve seen it, and it grows.” The rapturous reception led to the film being snapped up by Fox Searchlight, who helped make it Shelly’s first smash.

Another of her screenplays – Serious Moonlight, about a woman who holds her husband hostage after he announces he wants a divorce – was directed by Hines soon after, with Meg Ryan and Timothy Hutton as the leads. Roiff produced it with Shelly’s husband Andy Ostroy, but his feelings about it are mixed. “It wasn’t the same,” he says. “There was a magic to what Adrienne was able to do. Without her, it was that much harder.” Hines agrees: “Shooting that film was heavy, and very emotionally charged for me. I remember coming home one day to find my daughter playing with Adrienne’s daughter. And it was really beautiful to watch them together but also absolutely heartbreaking at the same time.”

Shelly’s spirit lives on not just in her films but also in the Adrienne Shelly Foundation, established by Ostroy to support female film-makers. Shelly once said she wanted to put out into the world only work that was “positive and decent”. Nothing better encapsulates this philosophy than Bernice’s mission statement in I’ll Take You There. “We’re responsible for each other,” she tells her hostage. “All of us. For what we do to one another.”

Sheedy laughs fondly when I remind her of the line. “That’s Adrienne,” she says. “That’s what she was like.”

• Waitress is at the Adelphi, London, 8 February–25 May.