Then she ran out of money.

"I was using 20¢ coins to buy groceries," Kapalos says. It felt as if a crisis were looming.

To industry observers, her move was baffling. Seven had given her a lifeline, appointing her the Sydney and Melbourne host of Today Tonight, after Ten brutally sacked her in its 2012 cost-cutting drive. A year later, she was at Sunday Night. A gig many TV reporters dream of.

Kapalos had worked for the ABC, SBS and every commercial network. Almost 23 years in broadcast journalism. She'd thrived in a profession biased towards younger women. Enjoyed a regular pay cheque. It was frightening to walk away.

But whenever she collapsed into bed, exhausted after another 15-hour slog, she thought about why she'd made this leap. There was her mother, Joanna, who died from cancer at 56 after doctors dismissed her "benign fibroids". The specialists, in 2013, who waved her away. (She was right to be concerned, given the large tumour on her right ovary. She returned to health after an operation.) But mostly, she thought of Dan Haslam.

In 2014, Sunday Night sent Kapalos to interview the 24-year-old, who had been fighting inoperable bowel cancer for four years. Haslam had been ravaged by chemotherapy. It burned his throat; made him so ill he couldn't eat for up to five days. The weight fell away. It was agony. "I already thought I knew the outcome of this story," Kapalos admits. "I went in thinking, 'This is about pain relief'."

Haslam certainly experienced that. His appetite returned; he devoured a steak and eggs the first time he tried marijuana. That halted his weight loss. "It's changed my life," he told Kapalos. His mother, Lucy, was stunned. "As close to a miracle as I've ever seen," she said.

Like most users of medicinal cannabis, Haslam ingested it as a specially prepared oil. (Not least because he set his moustache alight when he first tried a joint. "I made everything about it look so uncool," he recalled.)

Dan's father, Lou, was a retired drug squad detective. He never expected to become his son's dealer. Lou knew the risks: a hefty fine or a spell in prison. But he and Lucy faced a wrenching choice. They could break the law, or they could obey it – and watch Dan suffer.

In February of 2015, Haslam died. Kapalos attended his packed funeral – along with NSW Liberal premier Mike Baird, and conservative broadcaster Alan Jones. All had been moved by the family's campaign to see medical cannabis made legal in Australia.

One month after Haslam's death, Kapalos announced her resignation from Seven. Her Sunday Night report, she felt, was just the beginning. There was a bigger story here, and she needed to tell it.

Making a feature-length documentary isn't cheap. Kapalos did some crowd-funding, took out a massive loan (and is still paying it off). But the result – A Life of Its Own: The Truth About Medical Marijuana – was worth every cent.

Like many Australians, Kapalos had a negative view of marijuana. Over the years, she'd met people who seemed harmed by it. As a young SBS reporter, she even presented a story linking it to psychotic illnesses.

Then she interviewed the parents of children with intractable epilepsy. For them, cannabis oil was a godsend. It radically reduced their kids' life-threatening seizures, they insisted. And spared them further brain damage.

In A Life of Its Own, Attie Kolkman says her type of multiple sclerosis feels like "somebody hitting you with a sledgehammer". But now "I haven't got a mountain tall enough to stand on, to scream to the world [about medical marijuana]. It's given me the next 20 years."

Anecdotes like these, while impressive, weren't enough. Kapalos toured Israel, where the largest human trials of medical cannabis are run as a government program. She went all around Australia. She spent 18 months doing research, and interviewing dozens of doctors and experts.

All of which is essential when it comes to marijuana. One of the most feared, misunderstood – and widely used – drugs in the world.

Kapalos knew she'd encounter lots of questions. How could a parent let their toddler get high, people demanded to know. (They don't; medical cannabis oil is very low in THC, which is the psychoactive component of the plant. But it's rich in therapeutic CBD). Doesn't it make people psychotic? (No, CBD is considered non-psychoactive. While study results are mixed, evidence suggests high THC ingestion over long periods can aggravate existing schizophrenia in certain people.) Of course, people don't always know what they're getting through a black market – hence the push for legalisation and regulation.

Yet Kapalos is careful not to oversell the benefits. Medical cannabis not a cure-all, it doesn't work for everyone, and it has side effects. "The easy part was shooting the interviews ... I spent most of my time in the editing suite, making sure it was a balanced story."

She would have loved her mother to have had it; conventional pain medication did nothing in her final months. But there has been progress. Last year, Australia's Federal Parliament passed laws allowing the cultivation of medical cannabis. It was called "Dan's Law", in honour of Haslam's efforts. More recently, the Therapeutic Goods Administration announced medical cannabis would be legal – though strictly controlled – from November. "Until we see this translate into medication in the hands of patients," Lucy Haslam told Australian Story, "it's probably a bit too soon to call it a victory."

"This plant has thrown 'big pharma'," Kapalos says. "There's no money in it – and if there's no money in it, why would they pursue a clinical trial?"

While the film looks at current laws around the world, she hopes it will become a lasting document about medical cannabis. She is speaking from her hotel in Vancouver; sent by the Victorian Government to Canada and the United States to explore refugee resettlement options.

A couple of years ago, Kapalos worried about surviving in the tough world of commercial TV. But quitting – scary as it was – triggered an opportunity. While making her documentary, she met various politicians. In part, this led to her role as chair of Victoria's Multicultural Commission.

Four years ago – when Ten sacked her, minutes after finishing her Friday bulletin – she was left reeling. "I just sensed it was the beginning of the end of that era for me. I never felt like a victim, but it was really difficult."

Now, she has a job she adores. And almost two decades after making The Last Whistle, a documentary about the closure of BHP's Newcastle steelworks, she has another film to her name. One she made on her own terms.

"Sometimes," she says, "you don't recognise what an opportunity looks like until down the track."

A Life of Its Own: The Truth About Medical Marijuana will screen 4.45pm on October 15 at the Palace Como, as part of the Greek Film Festival.