Bella Ramsey spent many teenage years working with adults so never really went through the moody, rebellious phase often associated with being a teenager.

The British actor, who debuted in Game of Thrones aged 11 and uses they/them pronouns, says they had consciously decided not to behave like a stereotypical teenager after hearing criticisms from adults.

“I was like, I’m not going to be that.”

So when Sunny Dancer, a film about a summer camp for young people affected by cancer, gave Ramsey seven weeks to experience teenage freedom, it was an opportunity to dive straight in.

“I got to be a teenager aged 21, which was brilliant,” Ramsey tells BBC News. “It was really nice – and liberating.”

Looking back, Ramsey says the experience made them wonder whether they had missed out by being quite so sensible the first time around.

“I kind of wish that I had made the most of being a teenager and getting away with things and being a bit rebellious.”

In Sunny Dancer, Ramsey plays Ivy, a young female cancer survivor in remission who reluctantly heads to a “chemo camp” where she finds an unexpected group of friends and has a summer that changes her.

The rest of the cast were more than happy to help fill in the gaps; Ramsey says younger co-stars discussed songs and nights out.

“They were teaching me what being a teenager was for them and I was learning all the songs like five years later.”

Beneath the summer camp fun is a story that is deeply personal for the film’s writer and director, George Jaques.

His mother was diagnosed with cancer when he was 15, but it took another eight years for him to feel ready to turn some of those experiences into a script.

“I never seem to write in the moment I’m going through it,” Jacques says. “You have to sort of get through and understand it and have that reflection of it.”

He stresses that the film is not his family’s story, but “there’s bits of me” scattered throughout its characters.

Jacques was also conscious his own experience could only take him so far. So, he worked with the Teenage Cancer Trust, hearing from young cancer survivors as well as parents who had lost children.

“I remember going in to do a big talk with some young people who had survived cancer and they were like, ‘don’t call us kids, do not say we’re brave.'”

He says the film was “shaped” by these young people he met – such that he gave two of them roles in it.

Making the movie also forced Jaques to revisit some of his own fears around loss. He recalls a moment during the premiere in Berlin when emotion crept up on him.

“I remember seeing my mother and I realised there’s a version of that movie where my mum wasn’t sitting in the audience,” he says.

Both Ramsey and Jaques think we could be better at allowing people to experience grief without expecting them to quickly return to normal.

Jaques recalls losing someone close to him when he was 18, while sitting his A-levels.

“We are expected to just to carry on,” he says, describing the instinct to go “straight back to work and school”.

If we “really were honest with how we feel we might be able to understand it a bit better,” he adds.

In the UK, there is no general legal right to paid bereavement leave when someone close to you dies. The main statutory exception is parental bereavement leave and pay following the death of a child under 18 or a stillbirth after 24 weeks.

Ramsey thinks there can be an instinct to minimise what you are going through.

“You speak to people who are grieving, you’re like, ‘How are you doing?’ They’re like, ‘Oh, yeah, yeah, you know, it’s hard, but I’m fine.’ It feels very unhealthily British.”

After spending seven weeks playing a teenager who is desperate to be their own person, Ramsey’s advice for young people struggling to fit in is straightforward.

“Don’t try and fit in. Please don’t change to try and fit in because there are people who will fit in with you.”

Jaques agrees, but says the responsibility should not all be placed on young people to become more resilient.

“There’s so much pressure on young people to change on social media,” he says. “Why don’t we stop hating on young people? Maybe that’s where we should start as well.”