The girl's disturbing experience in the facility has been detailed in material filed with the Federal Court as part of a class action against the West Australian government over the treatment of up to 500 inmates.
In an affidavit, lawyer Stewart Levitt said the girl was 13 when first detained in May 2018 and spent various periods in Banksia Hill, the longest just under a year.
Mr Levitt alleged she was handcuffed and shackled when allowed out to see her parents and was routinely subjected to rough treatment, including having her head banged against a wall.
"She felt that she was being treated like a dog and responded to this by sleeping on the concrete floor and pretending that she was a dog," Mr Levitt's statement said.
"(The girl) had many violent interactions with officers when she was subjected to use of force for refusing to change into underwear or uniforms which had period stains.
"She would sleep on the bare floor rather than on a mattress because the mattresses were dirty with saliva and excrement.
"She was frequently subjected to strip searches and watched by officers while she was in the shower.
"She found these experiences distressing and humiliating."
Mr Levitt said the girl often reacted to her treatment by escalating her non-compliant behaviour and acts of self-harm, and when she was given access to education it was often at the kindergarten level.
His statement also detailed the treatment of a second lead plaintiff, an Indigenous teenage boy, who was diagnosed with schizophrenia in 2018 and spent a total of 55 days in Banksia Hill between 2014 and 2020.
It was claimed the teen was also confined to a cell for extended periods, was denied visits from his grandmother as punishment and was made fun of because of his intellectual disabilities.
He also experienced excessive use of force, including once, when he refused to return to his cell, being subjected to "folding up", where officers held him face down on the ground with his arms behind his back and bent his legs over so that his heels were near his buttocks, the affidavit said.
The Federal Court action alleges the two plaintiffs and others were discriminated against on the basis of their disabilities.
It claims Banksia Hill failed to assess them for mental health conditions when they were taken into custody resulting in impairments going undiagnosed.
It was alleged there was a failure to provide appropriate treatment, programs and services.
The action, launched in November last year, further claims that by being confined to their cells for up to 23 hours a day, the applicants were unlawfully imprisoned.
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