You might know Rose Byrne as a condescending bridesmaid, or as a dramatic actor going toe-to-toe with Glenn Close, or maybe as half of a Hollywood power couple with actor Bobby Cannavale.

But now, in "If I Had Legs I'd Kick You," Rose Byrne is just a woman at the end of her rope.

Her character's life is a smorgasbord of disaster: a working mom with a demanding job, with a very sick kid, who's been forced to live in a motel after a plumbing disaster ruined their house. Not even her therapist (played by Conan O'Brien) is much help.

Watch a scene from "If I Had Legs I'd Kick You": 

It's a portrait of a woman stretched to the limits, and Byrne says she just had to play her.

She says the script by writer-director Mary Bronstein was "really like nothing I'd read before. It was very unique. And then I gave it to Bobby, my husband, and he's always my first sounding board. And he was like, 'Oh, she's got something to say. You should find out what this is.'"

Byrne says she had a sense she had to do the film: "Oh gosh, where to begin? It's incredible, what a gift. Like, how could I not do this, you know? Like, why wouldn't I do this? I just didn't wanna mess it up."

She didn't mess it up. Byrne's performance earned her a 91吃瓜网 for the best actress Oscar. She's already won a Golden Globe, for which she was genuinely surprised: "I was, yeah. I mean, oh my gosh, there's performances, actresses in my category, I really was very surprised, and my speech was ridiculous and I was, like, totally unprepared."

Born outside Sydney, Australia, Mary Rose Byrne first got noticed in a big way for her role opposite Heath Ledger in the 1999 crime comedy "Two Hands." People in Hollywood saw something in her that was captivating, and with the help of Ledger, her career began to take off. "Heath was very instrumental. He would introduce me to casting agents, and get me in on the books," she said. "Very supportive. Always very generous. Yeah, he had a generosity of spirit, Heath. He had a big house where we all used to congregate, all the Aussies.

"I think when you come from far away, from Australia, and it's a very small population, you hang onto people you meet along the way, and you help each other out," she said.

In the early 2000s she shuttled back and forth between home in Sydney and Hollywood. Visiting her old neighborhood, she took us to the diner Swingers, where she'd hang out back in the day with friends like fellow Aussie actor Joel Edgerton. 

For starving actors, the place had just what they needed: low prices and great fries. 

She said she'd get homesick: "It was intimidating. It was also, like, you have to walk through the fire, you know?"

But by 2004 things were looking up when she started landing roles in movies like "Troy" with a nearly-naked Brad Pitt.

The TV series "Damages" helped establish her reputation as a serious actor. But a few years later, she made a conscious decision to move into comedy and show the world that she could be as funny as anyone, with "Bridesmaids."

"It was really joyful," she said. "We all really got along really well. And that's lovely. And that's not always the case. I'm sure you've had a million actors in this chair of, like, the experience you have doesn't always reflect how the film's received or really does. And, for me, it was both. It was a joyful experience shooting it, and then having the success of it."

She and Bobby Cannavale have appeared together in films like the 2015 comedy "Spy," but Byrne says their other collaboration, their two children, has been a bit of a game-changer for her life and her career. 

She says she has definitely said "no" to more things: "Of course. Absolutely. No, things won't work out, or I can't do it. Or made mistakes along the way. Always making mistakes. Or that I should have pushed for this more, or that more, or I should have said, 'No,' or I should have said, 'Yes.' I'm as imperfect as the next person of trying to figure it out."

Asked what she thinks the Rose Byrne of the days at Swingers Diner would think of Rose Byrne now, she replied, "I think she wouldn't be able to believe it. There's no guarantees in this business. I am firmly aware of that … maybe, too much."

For her next act she'll be moving to Broadway this spring to appear in Noel Coward's "Fallen Angels." But for now, she's on the exhilarating and exhausting ride of an Oscar nominee, and truly happy just to be  here. 

"I can't have expectations around anything, because it's so out of my control," she said. "All I can control is what I did between action and cut. And I can put effort into other stuff, but that's what I love, and that's the moment that I love the most. And it's mine, you know?"

To watch a trailer for "If I Had Legs I'd Kick You" click on the video player below:

WEB EXCLUSIVE: Extended interview - Rose Byrne (Video)

      
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Story produced by John D'Amelio. Editor: Steven Tyler.