Rhianne Barreto on her role as a teen struggling with the fallout of her sexual assault

Rhianne Barreto is in Cannes to present her dazzling lead performance in Share. The film finds her in steely, tightly-wound form, shrinking into the skin of Mandy, a teen whose life has become a waking nightmare since everybody in her school has seen a phone recording of her attack – but in person Barreto exudes a stirring liveliness, an energy that is enjoyably show-businessy. Towards the end of our time together, I ask her to tell me some of her favourite films. With all the winsomeness that she has displayed throughout our conversation, she immediately cites Singin’ In The Rain, adding that she relates to the Donald O’Connor song Make ​‘Em Laugh. I gently remind her about the somber subject matter of the film she is here to promote, and we both fall about laughing.

So what drew her to acting? ​“Let’s go right back to the beginning, baby,” she says, and proceeds to tell me a story about standing in for another actor at her sister’s leaving show when she was in year five. Her reply is hilariously wholesome somehow, and delivered with the wink-wink pretence that this school play had really been a kind of big professional break for her. ​“I was orphan number two, opera girl number five – fill-in jobs.” But someone went on holiday, giving her her chance. ​“I dressed up in my brother’s suit and put mud on my face.” A star was born. From there she attended the attended the Brit school and graduated to the National Youth Theatre, ​“and the rest of my life has been this film… either preparing for it, making it, or doing press for it.”

Share is a bold, somewhat experimental film, and the lead role an obvious gift to an actor. Barreto is in pretty much every scene, and has the doubly difficult challenge of being both the film’s protagonist and its unflinching moral compass; on top of this, her task, which she pulls off, is to make Mandy a strong character while never lurching into drama or sentimentality. Still, this puts Barreto in an invidious position, of which she seems all too aware, of struggling to find another project to match its challenges and intensity. But she’s resilient, ​“I’m at a point early in my career where I have the internal power to say, ​‘No, I’m going to wait for something really good… something scary and challenging’.”

Barreto, 21 and from West London, speaks with a particularly English brightness, like somebody who went up for the position of Head Girl at school but ultimately failed to make the grade because she wasn’t quite serious enough. She’s confident, looks you right in the eye, and at no point seems to betray any nerves about being in Cannes for the first time in her nascent career. ​“It’s like adult Disneyland!” she exclaims.

Barreto is clearly very serious about her craft. She’s also good on the challenges of her character, and the act of internalising her pain, drawing parallels with the Danish film The Hunt, in which Mads Mikkelsen’s protagonist is falsely accused of a sexual crime. ​“These characters are coping and coping, and dealing with something that happened to them… they’re victims, but not crushed. It’s about finding that balance.” In Share, Barreto offers a conspicuously modern performance, all introspection and discomfort, giving a sense of somebody who is still struggling with the effects of her attack, as it is repeated on social media. In her tightly coiled body language, and the subtle defiance, she projects somebody caught in a world that is hostile at every turn. From the films she watched with her director, Pippa Bianco, to her some-time isolation on the film’s set and continued friendships with other actors, it’s clear that this film has been a labour of love for her.

What is she drawn to, as a performer? Barreto surprises me by telling me she’s looking for something along the lines of Good Will Hunting. ​“There’s that scene with Matt Damon and Minnie Driver, where it goes from them being really happy in love to screaming at each other. That is beautiful – that progression, that amount of drama, and knowing you have to get to that place.” Her eyes light up, as she considers the acting challenge of working your way through those stages.

Our interview starts to peter out. Or rather it’s not really been an interview somehow, as Barreto has sort of taken chummy control of the situation, and for every three questions I have asked her she has consistently asked me one back – ​“How’s your Cannes going?” ​“What are your favourite films?” and followed these up with further questions. We walk towards the festival together, talking about Some Like It Hot, my favourite film, and about her plans for the day – the film’s premiere, her dress try-out. We’ve had a little time in each other’s presence, but I feel genuinely warm towards her as we part, at her hotel gates, like temporary friends at summer camp.

Share premieres in America on HBO on 27^th July