The father of a severely malnourished girl who is on trial for allegedly starving her told authorities she had a "fantastic diet" and he had no concerns about her health, a Perth court has heard.

Both the girl's parents are charged with engaging in conduct which resulted in their daughter suffering, with the District Court hearing she was dangerously underweight at just 27 kilograms when she was eventually admitted to hospital aged 17 in 2021.

This happened after two dance teachers raised the alarm, concerned that she was too skinny and her health was at risk.

One instructor described an emotional confrontation with her father not long before she went into hospital.

"I said 'she's using her bones to dance'," she told the court.

"She had nothing but bones to dance with.

"I had tears in my eyes."

Girl was never alone

In 2020 the teacher rang the Department of Child Protection, telling them she believed the parents were starving their daughter, who had "the body of a 10-year-old", even though she was 16 at the time.

The teacher was initially advised that the girl should herself be asked if she felt unsafe, and told how to contact child protection workers.

But the court heard it was hard to speak to the child alone, because her mother was always at the dance studio with her.

Child protection worker Zivana Petrovic said investigations showed the girl had never attended a public hospital in Perth, and was registered for home schooling.

She said the girl's father told the department his daughter had a "fantastic diet and [was] getting stronger".

She had "good energy", was dancing up to eight hours a week, and he had no concerns for her health.

He said she didn't need an independent medical assessment, and while he knew "people were saying she was underweight", she "had the right diet".

No idea about periods

He claimed that while she hadn't been through puberty by the age of 16, she "could do so later".

Ms Petrovic told the court the girl was in "early stage puberty", and the department had been made aware of a conversation at the dance studio in which the girl appeared to admit she didn't know what a period was.

The department had also been in contact with the girl's previous dance teacher, who held similar concerns about the teenager's weight and lack of muscle development.

The trial of the parents is continuing.