Posting photos of herself with the hashtag #challengeaccepted, the thirty-something woman quickly became the breath of fresh air in a stiflingly humourless community of retouching and unsolicited advice.

You might know Barber from her acting career in Australian television. She has appeared in a smattering of comedies and had a four-year stint on prime-time drama All Saints.

But since 2015, Barber has also been parodying and poking fun at photo shoots in which models look glamorous sitting on toilets, or laying in piles of dirt in their underpants in states of rapturous ecstasy, and here is where she has found an audience of millions.

“In the Instagram world, it started out as being pretty, and filtered, and glossy, and sponsored. And wow,” Barber tells Saturday Extra ahead of the release of Challenge Accepted, her debut memoir.

“It’s a handbrake to that filtered life,” Barber says of her own career that’s seen her artfully replicated “break the internet” shots such as Hailey Baldwin sitting on a toilet and Beyoncé serenely holding her newborn twins, surrounded by flowers.

“There’s people now, like myself, who are showing the other side of it.

“That’s why it has resonated. Like, ‘thank God I don’t have to be on a yacht picking up my kids from school.’ ”

Barber decided to parody some of the most ridiculous shoots she’d seen in her Instagram feed while chatting with her sister.

“I just wanted to make people laugh,” she says of the account.

Long-legged and tanned, Barber is pretty faced, but often gives a blank and bored stare. Her clothes sometimes appear to be creased and the settings she chooses are suburban and anti-aspirational.

The captions can be brutal, serving to remind us that these original posts are about selling us things we don’t want, or need.

Within weeks she had a few thousand followers and the ABC contacted her for an interview.

That weekend, a group of friends came to her home for drinks and she heard that a newspaper had republished the story on its front page.

Amused, her friends created a drinking game for every time she gathered another thousand followers. Within a minute her followers had jumped to more than 15,000.

The next day, she woke with a hangover to discover that more than 50,000 people were following her. The account now has 4.8 million followers.

“The people I am having fun with are some of the most privileged people in the world.

“It’s showing an alternative as opposed to the norm, which is just a gorgeous, good- looking model,” she says.

Barber’s popularity speaks to both her humour and her ability to transform the ridiculous into the relatable.

As her success has exploded, Barber has been in talks with Screen Australia about a project and has sold out seven dates of a 36-city US comedy tour.

But it has been a long road to fame, with many tortuous twists. In her book, Celeste details a year-long period of relentless girl-on-girl bullying, kicked off by a dramatic and violent event.

A friend’s older sister manufactured a rivalry between the two, corralling the entire school into watching the pair fight at lunchtime.

Barber writes about the encounter as being long, terrifying and lonely.

The girl circled her and attacked her before a terrorised Celeste ran and took shelter in the library and began writing her first comedy monologue.

The event started a year-long campaign of bullying and manipulation by a group of mean girls that left Barber isolated and confused.

Her experience with the school bully illustrates, she says, how girls and women tend to focus on their insecurities, and how that plays out in misplaced unkindness to one another.

She ultimately found the experience edifying.

“My stuff was frightening,” she says. “But I was resilient and I’ve always had a mouth on me.

“I just don’t know how I would cope if my boys went through (what I went through). I’d lose my shit if I heard my kids were getting bullied.”

Ironically, the girl who terrorised the young Barber once wrote an article about being bullied at school.

“She’s written an article once about how she was bullied at school and I’m, like, ‘No, I don’t remember that.’ Everyone has their own experience but it’s kind of, like, ‘You were after me.’

“She’s written about accepting each other but it’s kind of just body-shaming really. It’s bullying, in a whole new way.”

Barber has been well- received in Australia, but is absolutely adored in the US.

After her Instagram posts went viral, Celeste describes the first trip she made to LA where she was wooed by a slew of would-be managers, all dazzling her with trips to exclusive hot spots and restaurants.

She details the smoke and mirrors employed by the tinseltown deal-makers and of being taken to the best parties and introduced to the biggest celebrities. She says their tactics were designed to convince her that — “if you go with me, you’ll be constantly working with the best”.

At one meeting, she says, a manager casually, yet confidently, offered her the gig of hosting the Oscars the following year.

At another meeting at West Hollywood’s exclusive Soho House, she says she saw former Spice Girl and Australian X Factor host Mel B in an argument with a valet about the cleanliness of her car.

But Barber says she has become accustomed to the business side of internet fame.

“It’s always kind of been a hustle thing for me,” she says.

Celeste describes being diagnosed with ADD/ADHD (attention deficit disorder/attention deficit hyperactivity disorder) — she says she’s still too distractible to be able to properly remember — as the greatest thing that could have ever happened to her.

“When I was diagnosed with ADD and put on medication I was like, ‘Holy shit this is awesome.’

“And it came at a really good time for me because I knew what I wanted to do because I couldn’t concentrate. Everything just kind of clicked,” she says.

Despite her positive experiences with the diagnosis and medication, Barber is critical of parents who are quick to medicate their kids when they misbehave or express disinterest in their schoolwork at a young age.

“I hear so many people say, ‘Oh they’re really loud and they can’t sit still and we’re looking at getting them on Ritalin.’ I’m like, ‘He’s six! Of course he can’t sit still.’

“School is boring! School totally sucks. Not that I’m saying it is an easy out. It’s case specific.”

In the wake of being diagnosed at the age of 16, Barber details in her memoir, how she lost her appetite and a “shit ton of weight”, which gained her a “shit ton of respect,” at high school, a phenomenon she describes as being sad.

She concealed the fact she was taking prescription drugs from her peers and described the secrecy as “exhausting”.

The hashtag #noregrets is popular in the Instagram community, but Barber says she prefers confronting the reality of life when it comes to friends, family and her career.

“I think (no regrets is) a cliche quote from back in that day and it’s gone too far,” she says.

Her book includes a long and detailed list of moments in her life when she wishes she’d behaved differently.

She highlights particular moments around family and her relationship with her husband Api, whom she has lovingly dubbed #hothusband and features heavily in her posts.

She also regrets certain key moments in her career when she feels she didn’t work hard enough and missed opportunities.

“I’ve never understood the idea of, ‘I don’t live with regrets.’ Really? You haven’t f...ed up and thought, ‘That was dumb’? Ever?

“That blows my mind, that there are some people out there who genuinely go, ‘No, everything I’ve done is great.’ No, maybe it’s not. It’s not (that way) for me.

“People ask me for advice and I always say, ‘No’. There’s enough people online who think they’re doctors, giving advice. Just do what you’re doing.”