Mastrosa, 34, issued an advance release of the novel – which the BBC has chosen not to name – to 21 readers in March last year before a complaint about its content was made to police.
Chisholm read the whole book, published under the pen name Tori Woods, and found a reasonable reader would find it “undeniably offensive”.
Throughout the novel – the cover of which is pastel pink with the title spelled out in children’s alphabet blocks – the protagonist uses child-like language, wears children’s clothing, and engages in child-like behaviour.
Chisholm said any references to the character being 18 were insufficient to overcome the implication of her as a child.
“Importantly, those descriptions and language are used in the portions of the book to describe a character similar to a young child when the sexual activity is occurring,” Chisholm said, according to the Australian Associated Press.
“The reader is left with a description that creates the visual image in one’s mind of an adult male engaging in sexual activity with a young child.”
Found guilty of one count each of creating, possessing and distributing child abuse material, Mastrosa will return to court to be sentenced on 28 April.
When Mastrosa was charged, BaptistCare told the Daily Telegraph she had been stood down from her role pending an investigation.