"It says 'Advance Australia Fair' and when it was originally written it meant advance Australia for white skin people," Harper told SBS News on Wednesday.
"And when it says 'we are young' it means that it ignores the Indigenous Australians who were here before the English for over 50,000 years."
Harper said she had chosen to take a public stand on the issue at her school "because I feel that this is the right thing to do and it will help raise awareness for the issue."
While the schoolgirl said media attention had been strange, she was unbowed by the criticism from Senator Hanson and others. Asked if it worried her, she said, "not really, no."
Her father, Mark Nielsen told SBS News he and his wife strongly supported their daughter's actions.
“She decided that it’s something she felt very passionate about and it’s how she decided to deal with it," he said.
“She’s a very unique individual.”
The protest earned an extraordinary attack from Senator Hanson, who posted a video on social media calling for the “brainwashed” “brat” to be kicked out of school.
“I’d give her a kick up the backside,” she said. “This kid is headed down the wrong path and I blame the parents for it, for encouraging this. No. Take her out of school.”
Senator Hanson said Indigenous sports stars have stood on the winner's podium with the national anthem being played in the past.
“If it’s good enough for Cathy Freeman, Johnathan Thurston and Warren Mundine to stand for the national anthem, it should be good enough for this nine-year-old brat,” she said.
In a statement, the school said it said it had met with the student and her family to discuss the issue and suggested alternatives.
“The school has been respectful of the student’s wishes and has provided other alternatives to singing the national anthem. State schools set out clear standards of behaviour that they expect from their students in their Responsible Behaviour Plan for Students,” the statement said.
At school, Ms Nielsen was told she could stand for the anthem and not sing it, or leave the assembly area while it was sung. But the standoff continues as Harper said the school’s alternatives do not work for her.
“She feels that by passively sitting, quietly sitting, it’s her best way of engendering change and thoughtfulness about what’s going on,” her father said.
The national media attention following Wednesday morning’s story in Brisbane’s Courier-Mail took the family by surprise, and even before Senator Hanson’s intervention had led to some backlash as well as support for Harper.
“Yes, apparently I’m one of the worst parents in the world,” Mr Nielsen said, but added he was not upset by it. “People are entitled to their opinion.”
The family is not Indigenous but Mr Nielsen said that social justice and Indigenous rights are a big topic of conversation over the family dinner table.
“I don’t want this to be a situation where the school gets vilified, that’s not fair,” he said.
“This is a much broader issue about having a dialogue over what is our national anthem what words are in it, and what they mean to different people. I’d like to it to be about that, not about a strong-minded nine-year-old girl and a school which has to deal with its own set of rules and regulations.”