While the press release from this week and the trailer don't explicitly say that Ziegler's character is autistic, it had been previously reported in an August 2018 Rolling Stone profile of Sia along with other details about the musical film.
Ziegler, who was notably in Sia's music video for "Chandelier", plays a non-verbal autistic girl named Music.
Sia has been hit with criticism about her new movie, Music.
It all started when Irish actress Bronagh Waugh asked Sia why the character wasn't played by an autistic actor.
The phrase "cruel, not kind" went viral, with many online users removing the context of her original phrase.More news: Hawaii imposes new COVID-19 travel restrictions
They have also pointed out the irony of a movie about disability, with no captions for hearing impaired viewers.
But soon after the trailer dropped, backlash ensued thanks to Sia's casting of 18-year-old Ziegler - who is not on the autism spectrum - as a teenager called Music, who has non-verbal autism.
She added that she tried to work with a disabled actor, but it didn't work out: "I actually tried working with a a lovely young girl non verbal on the spectrum and she found it unpleasant and stressful", Sia tweeted.
"I love Maddie Ziegler, don't get me wrong", one fan said of Sia's movie.
"I cast thirteen neuroatypical people, three trans folk, and not as fucking prostitutes or drug addicts but as doctors, nurses and singers". "F--g sad nobody's even seen the dang movie".More news: Kanter traded to Portland and Hezonjia to Memphis in a three-way deal
The main thing the star wanted people to understand is that her "heart has always been in the right place" when she created the film. "The first is obvious - that it inevitably, no matter how hard it tries, mistranslates the experience of being autistic".
According to her, many of her friends have disabilities and they are some of the coolest, most talented, funny, kind and intelligent people she knows.
One person said: "Autistic people do not bring their families or carers suffering, in fact it's often caregivers who cause harm to disabled people. autistic people need to be allowed to tell their own stories, not this garbage".
Grrrrrrrrrr. Fuckity fuck why don't you watch my film before you judge it?
Sia's response to criticism about her new movie.More news: UK’s Prince Harry welcomes Princess Diana interview inquiry
After tweeting out the trailer, however, Sia was criticised for the decision to cast an "able bodied & neurotypical" actor to represent an autistic character, and for the film's seemingly "infantilising" tone.