Emma Taylor spent her whole life believing that something was wrong with her.

"I've always been called weird or a little bit strange. One of the regulars at work calls me Fruit Loop. It was just something I was used to," the 27-year-old said.

Key points: For every girl diagnosed with autism, four boys are diagnosed

For every girl diagnosed with autism, four boys are diagnosed The real ratio may be closer to one girl for every two boys

The real ratio may be closer to one girl for every two boys Clinicians have drawn up new guidelines so girls with autism don't miss out on a diagnosis

But when her six-year-old daughter Felicity was recently diagnosed with autism, Emma came to a startling realisation.

"I was reading through her autism checklist, and I thought, 'Hang on a minute, I'm checking every single box here too'. I was checking 99 per cent of these boxes, and I began to wonder whether maybe I had it as well," she said.

Emma had friends in high school, but often found socialising draining. ( Supplied: Emma Taylor )

Shortly after Felicity's diagnosis, the Ipswich-based mum who works as a gaming attendant booked herself in to see a clinical psychologist.

"The psychologist said to me, 'You're a clear case of Asperger's … and you have had it your entire life.' For me, that was a relief," Emma said.

Emma's childhood was marked by odd behaviours that concerned her mother, but were dismissed by the family doctor as "quirkiness".

If she had a packet of lollies, she felt compelled to divide them by colour before she could eat them.

She could not help but mimic people's accents and mannerisms.

She had lots of friends at school, but found socialising so draining she would sometimes come home, sit on the floor and stare into space.

"Everyone thought I was daydreaming, but my way of recharging was shutting down. I just needed nothingness," Emma explained.

Girls with autism flying under the radar

Emma says her Asperger's diagnosis has come as a relief. ( ABC News: Barbara Miller )

Like many Australians, Emma wrongly assumed autism was an exclusively male condition.

The stereotype of the boy genius who cannot make eye contact is so widespread that experts believe many women and girls with autism are going undiagnosed.

"For a few decades now, we've believed that for every girl on the autism spectrum, there are four boys," said Dr Michelle Garnett, a Brisbane clinical psychologist who specialises in autism diagnoses.

"We now think the ratio is one girl to every two boys. That's many more girls than first thought."

The main problem for clinicians is that women with autism are often the ultimate chameleons, able to observe the dynamics of any social situation, and perform what they believe is required of them.

"We need to give them an Oscar for that performance," Dr Garnett said.

"But even though we see that beautiful mask, often they get home, they're so exhausted, they're melting down, they can engage in self-harm from a very young age, and they start often to isolate themselves."

Professor Andrew Whitehouse from research group Autism CRC has drafted a new set of diagnostic guidelines to help clinicians identify women who may be flying under the radar.

Common signs of autism in girls: A desire to interact with others

A desire to interact with others A tendency to mimic others in social situations

A tendency to mimic others in social situations Passivity, often perceived as "just being shy"

Passivity, often perceived as "just being shy" One or few close friendships

One or few close friendships A tendency to "camouflage" difficulties

A tendency to "camouflage" difficulties Developmentally appropriate language skills

Developmentally appropriate language skills A vivid imagination

A vivid imagination Less severe and frequent repetitive behaviours

The guidelines would alert doctors to the predominantly female markers of autism.

"The end goal is to provide every person the optimal start on their autism journey, irrespective of the background, geographic location, or indeed their sex," Professor Whitehouse said.

The guidelines have been submitted to the National Health and Medical Research Council for endorsement.

A diagnosis could be a lifesaver for women and girls with autism, according to Dr Garnett.

"They often have no idea who they are behind the mask," she said.

"That leads to enormous difficulties in depression, but also in social anxiety, generalised anxiety disorder, and obsessive compulsive disorder. Anorexia nervosa is overrepresented by far in our girls with Asperger's syndrome and autism."

Like daughter, like mother

"I could always see echoes of myself in her," Sarah says of her daughter, Izzy. ( ABC News: Barbara Miller )

For Sarah Stokes and her 14-year-old daughter Izzy, their twin diagnoses have been liberating.

"I always wondered why I didn't react and behave like everyone else. I just thought I was a really bad kid. And then the doctor told us, you have autism," Izzy said.

"I finally figured out what was going on. I could finally get help."

Izzy was diagnosed four years ago, prompting her mum to finally confront the possibility that she was also on the spectrum.

"I wanted answers to a lot of things that had happened in my life," Sarah said.

"A lot of damage can be done when teachers and families have treated someone as though they're naughty and weird. People shouldn't have to feel like that."

Armed with a diagnosis, Sarah has forgiven herself for being unable to finish university when she was younger.

"People just instinctively knew that I was different," Sarah says. ( ABC News: Barbara Miller )

"I spent most of my life thinking I was a complete failure … but now I can see why that happened. If a lecturer gave me a reading list, I had to read every book on it," she said.

"I got more and more behind with my assignments because I was getting bogged down in all the detail."

She is now studying by distance, which allows Sarah to set her own pace.

She has also helped Izzy come up with coping strategies so she can still move through the world without getting overwhelmed.

"I just thought I was a really bad kid," Izzy says of her life before being diagnosed with autism. ( ABC News: Barbara Miller )

"I'm still not like other kids, but I understand why I do things now," Izzy said.

"So if I want to go to the shops with a friend, I give myself a pep talk, like, 'Hey Izzy, you can do this. They're people, just like you'.

"I just try not to touch people, and I try and stick close to my friends."

Izzy has what few teenaged girls do — a mother who totally understands her. Their shared diagnosis has brought them closer.

"She says I'm her best friend and I understand her more than anyone else," Sarah said. "I think she knows I've got her back."