Sia has addressed her casting of Maddie Ziegler in her film Music again, describing the decision as “nepotism”.

The singer was on the receiving end of a backlash from the autistic community last year for casting her frequent collaborator over an autistic actor.

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Music centres around an autistic teenager, played by Ziegler. Critics argued that Sia should have given an actor with experience of autism the opportunity instead and to not have done so was ableist and could perpetuate harmful stereotypes of autistic people.

She was also criticised for consulting with the organisation Autism Speaks on the film, which has been widely condemned within the autistic community for spreading misinformation, its negative characterisation of the condition in promotional materials, and its practices. In response, Sia said she had “no idea it was such a polarising group”.

Speaking on the Australian TV show The Sunday Project, Sia responded once again to the controversy surrounding the movie. “I realised it wasn’t ableism,” she said of her casting decision.

“I mean, it is ableism I guess as well, but it’s actually nepotism because I can’t do a project without her. I don’t want to. I wouldn’t make art if it didn’t include her.”

She went on to say she considered herself as Ziegler’s “bonus mum”. The pair have worked together for years, with Ziegler appearing in Sia’s music videos for ‘Chandelier’ and ‘Elastic Heart’, as well as live performances.

Sia added that Ziegler had expressed concern on the first day on set that viewers would think she was “making fun” of autistic people. “I bold-facedly said, ‘I won’t let that happen,’” explained the musician.

“Last week I realised I couldn’t really protect her from that, which I thought I could. We sent it off to the Child Mind Institute and she received 100 percent as performance accuracy. I realise that there are some things I can’t protect her from as much as I try.”

Previously, Sia had responded to the backlash over Ziegler’s casting in November, saying she had tried to work with an autistic actor but they had “found it unpleasant and stressful”. When an autistic actor replied to her saying they could have managed the role, Sia told them: “Maybe you’re just a bad actor.”

She later reflected on her response, noting that she “should have just shut up”.