Brie Larson is just 25, but she has already lived half a dozen eventful lives. A full 10 years ago, she released an album and scored at least one near-hit single. She’s directed a short film. She has designed her own font and remains interested in the science of typefaces. Yet none of these areas of expertise makes up the official day job.

“I always take a guitar to set and make music,” she says. “But acting is still top of the pyramid, I suppose. That’s focus number one.”

Having reached her current great age, Larson is finally in danger of becoming a proper star. Not many people saw 2013's Short Term 12 – by my reckoning, her 25th film – but the study of life in a care home for troubled teenagers won the sort of reviews that make careers. She went in still scraping a living. She emerged as a hot property.

"Yes. Until then it really was feast or famine," she remembers. "Even while shooting Short Term 12, I was broke. I was taking home food from set. We were all living off the food on the service table. It was a really bizarre situation. Then it turned."

Her performance as the home’s supervisor is a beautifully honed exercise in unhurried naturalism. If there’s a trick to what she does, it’s to do with how, despite sliding quietly into a scene, she still manages to draw the eye.

Folk noticed. Following many nights of red-eyed labour, Larson looked to have become an overnight success.

“After the premiere, my life completely changed,” she says. “It has never been the same. Before that I was ‘trying to be an actor’. Afterwards, people really saw me as a proper actor. I can finally choose the projects I want.”

One of those projects, Rupert Wyatt's The Gambler, tumbles into cinemas this week. As we speak, she is finishing work on our own Lenny Abrahamson's follow-up to the magnificent Frank. In Room, an adaptation of Emma Donoghue's successful novel, she plays a woman held captive with her young son in a small room for many years.

Larson admits it was a troubling story to engage with, but it seems that Abrahamson worked hard at lightening the mood.

The man from Kerry

“I love Lenny so much,” she says. “There are certain days when it is very dramatic and – I am not very familiar with Ireland – but he comes on set as a different person. He is a senator or some sort of business official. Maybe he is the mayor of a place called ‘Kerry’. Is that right? He’ll spend the day walking round saying: ‘Are you from Kerry?’ That cracks me up.”

(Having talked to Abrahamson, I can confirm he was not impersonating the person you probably think. So it’s safe to publish the anecdote)

So is this the kind of story that hangs around with an actor when he or she goes home? Does it lurk around in the quiet moments? “It brings more awareness and I feel humbled by that. You see how many different ways a life can go. I am basically just a great empathiser. That is what my job entails.”

In some senses, it must have been trickier to spark up the empathy in The Gambler. Wyatt's follow up to Dawn of the Planet of the Apes takes an unexpected swerve into urban low-life territory. In this remake of Karel Reisz's 1974 movie, Larson plays a decent – but ill-defined – girl caught up with Mark Wahlberg's fallen intellectual.

“It didn’t feel incomplete or fragmented to me,” she says. “Whether or not that matters to the audience doesn’t matter so much. A woman’s mystery is the most exciting part.”

What about the film’s insights into the world of illegal gambling in Los Angeles? If William Monahan’s script is to be believed, casinos lurk behind every second suburban home.

“I learned quite a lot from Rupert and Mark, who are way into it,” she says. “I didn’t even know that these casinos existed. But when something gets in your brain you can’t shake it. Suddenly, I was seeing them everywhere in LA. I’d see houses I thought were for sale and there’d be these people lurking outside at night. What’s that?”

Larson appears to have the sort of restless mind that a young actor needs to keep fresh. If earlier interviews are to be trusted, she has always been that way. Born in Sacramento, she moved with her mother to LA after her parents, both chiropractors, broke up. She seems to have tried everything as a kid. I can imagine she must have been exhausting to live with.

"It was a combination of being ridiculously creative and just trying to do everything," she says. "I was ice-skating. I was drawing storyboards, I was dancing. I remember I made this 400-page storyboard for The Lion King. My mom wouldn't let me bring it. I was really upset, but I ended up talking to the animators and they gave me their card."

So, what about this tale I have heard that, when young, she took to eating her dinner in the shower. Is this not the point where creativity morphs into madness? “That’s true. Sometimes you take a snack in the bath. That’s not too strange. I don’t ever think that something is a crazy idea until I explore it.”

She pauses to gather her thoughts. “Just because eating potatoes in the shower doesn’t work for you that doesn’t mean it won’t work for me.”

There’s a maxim to live life by.