Sarah Bolger on what it’s like to play a psycho in ‘Emelie’

Sarah Bolger is so busy that she never gets back to her home in Dublin.

“I have a dog, a poor dog. It stays with my family,” the actress tells us, laughing. The dog, a she, is a rescue, which accounts for her name, which was not Bolger’s choice. “Don’t judge me: Her name is Fluffbucket.”

Bolger is really personable, giggling at everything, which stands in stark, amusing contrast to her new movie. In the indie thriller “Emelie,” she’s the title character: a mysterious young woman hired as a last-minute babysitter for three young kids. Once the parents have left for date night, Emilie starts acting strangely. She encourages the kids to destroy the house, then gradually reveals an ulterior, sinister motive. It’s a dark role that goes to some deeply messed-up places.

“That was the sick, twisted part of myself that wanted to do it so badly,” Bolger confesses. “I just loved this girl. I read the script and was like, ‘What the f— is she doing? What’s her deal?’ I couldn’t understand. She is broken. A glass has smashed inside herself.

“She’s not a real person. To me she’s almost mythical. She’s a lie within a lie buried beneath lies,” she says. But she draws the line at her being insane: “I wanted to make that clear in the movie. She’s just not whole.”

Going “there” can’t be easy over an entire shoot. “It messed with my head a little bit,” she admits. “I’d go back to my hotel room in this isolated town we were filming in. I would have to sit down at night and wrote a diary — for lack of a better word — breaking down what she went through for the scenes every day.”

Bolger was a child actress who broke through with 2003’s “In America,” in which she starred alongside her real-life sister, Emma, as sisters who emigrated with their parents (Samantha Morton and Paddy Considine) to New York in the 1980s. Here, she got to act with a new generation of child actors.

“These kids were so professional! I don’t know if I was that prepared at their age,” she says.

Director Michael Thelin actually kept her mostly separate from the kids. “He didn’t want them to feel too comfortable around me, like I was their friend,” she recalls. “I would go back to my trailer, alone, go on set, not talking to anyone, then go back to my hotel room and write in this poor girl’s dairy. It was a lonely month and a half.”

It was demonstrably different from making “In America” a decade-plus ago. For that film she and her sister lived in director Jim Sheridan’s house for a month prior to filming.

“We were a big family. Nothing was scary,” Bolger remembers. “We were playing dress-up in our real life and he would take what we were doing and add it into the scenes. It was very organic — whereas this movie should never be organic to anyone. No one should experience what we did in the film.”

Bolger is one of countless child actors who continued acting into adulthood. She’s now 25, though she admits she still looks young, meaning she still gets high school and college roles. (She was the latter in last year’s football movie “My All-American.”)

“It’d be fun to play someone who’s a woman,” Bolger says. “College roles are wonderful, but to have the voice of a woman, it’s a goal for me in life and onstage. I have to become a woman now.”

She’s at least been getting more mature roles, with stints on TV like “Into the Badlands” and “Agent Carter,” one of Marvel’s many shows.

“When I got the job, I got a Marvel.com email saying, ‘Sign your [Non-Disclosure Agreement],” she says, once more giggling. “I was so f—ing excited. Marvel emailing me!”

Follow Matt Prigge on Twitter @mattprigge