"Looking back, I should have just shut up; I know that now," the singer recently told Australia's the Sydney Morning Herald. She doubled down on her decision at the time.
"It was 3 in the morning, and even though I have a rule that I don’t do anything emotional past midnight, I (expletive) up this time."
The film features Kate Hudson as Zu, who takes in her half-sister Music (Maddie Ziegler), who has autism spectrum disorder. Leslie Odom Jr. stars as a neighbor who assists with caring for Music.
Ziegler's casting prompted scorn and accusations of ableism, which is defined as discrimination against those with disabilities.
One of Sia's critics tweeted at the time: "Several autistic actors, myself included ... We all said we could have acted in it on short notice. These excuses are just that- excuses," @HelenAngel wrote on Twitter. "The fact of the matter is zero effort was made to include anyone who is actually autistic."
"Maybe you’re just a bad actor," Sia wrote back. In another reply to the same tweet, she wrote: "You have no (expletive) idea because you weren’t there and haven’t seen the movie."
Sia also told the Herald that she sought someone on the autism spectrum out for the role but that they thought the film was too upsetting.
The singer-songwriter has heaped praise on 18-year-old Ziegler, an alum of Lifetime's "Dance Moms." Sia says the teen poured her heart into the role of Music, careful to portray the character in a respectful way.
The two previously worked together on Sia's single "Chandelier."
"Maddie is the reason the Twitter comments profoundly affected me," Sia told the Herald. "She had researched her role for two years, we watched movies together, and I taught her the nuances and ticks I had observed from (a) friend (with autism). We did this in the most sensitive and respectful way. She was worried people would make fun of her. I promised her I wouldn’t let that happen."
Contributing: Gary Dinges
Further details on the casting controversy: Sia, after being criticized for ableism, defends portrayal of autism in new film
This article originally appeared on USA TODAY: Sia walks back autism casting comments after criticism for ableism