Days after Justin Trudeau told the United Nations that his government was working hard to improve the quality of life for indigenous peoples in Canada, it has emerged that his government spent more than C$110,000 ($88,000) in legal fees to avoid spending C$6,000 on orthodontics for a First Nations teenager suffering from chronic pain.

The figures, released through the Access to Information Act, were made public by the Canadian Broadcasting Corporation on Friday. They relate to a continuing court battle that has pitted the federal government against Josey Willier, a teenager from Sucker Creek First Nation, who for two years complained of chronic headaches and jaw pain stemming from an impacted tooth and a severe overbite.

In 2014, two orthodontists warned that without braces, Willier would eventually need invasive jaw surgery. One noted that Willier’s condition would probably worsen and could leave her with difficulties in eating and speaking.

For help in paying the C$6,000 treatment, the family turned to a benefit program run by the federal government – which covers the cost of health services, basic dental care and orthodontic treatment when medically necessary for First Nations people living on reserves.

The family’s request was denied by the Health Canada, who said her condition was not serious enough to warrant braces. Three appeals of the department’s decision proved unsuccessful.

With the help of a lawyer working pro bono, the family took their case to the country’s federal court, where a judge determined that the denial of payment was “reasonable”.

During a span of 16 months, the federal government spent at least C$110,336.51 in legal fees to fight the request for payment. The legal costs are likely to rise, as the family filed an appeal of the federal court decision in June, arguing that it failed to take into account the chronic pain suffered by Willier as well as the eventual need for surgery.

“I think it’s atrocious,” Cindy Blackstock, whose First Nations Child and Family Caring Society intervened in the case, told the CBC. “As a taxpayer, I’m absolutely floored that Canada would spend $110,000 defending [against] a $6,000 investment to help a child. They could have used that money to buy 18 children in medical need the orthodontic services they needed.”

In a statement to the Guardian, Health Canada pointed to the process used to assess the claim. “In this case, the issue is not about the monetary value or affordability of the claim,” it said. “Like all requests for coverage of orthodontic treatment, this case was reviewed by a licensed orthodontist when it was initially submitted for approval, and subsequently reviewed by three other licensed orthodontists during the appeals process, all of whom agreed with the initial assessment. The evidence did not support the request for coverage.”

The department said its plan covering First Nations children was more generous than the private plans held by most Canadians. Dental care – save for surgical-dental interventions and a few prevention programs aimed at children – is not included in Canada’s universal healthcare and instead is often funded through private insurance or out of pocket. A 2014 report noted that Canada provides one of the lowest proportions of public funds towards dental care among OECD countries, contributing 6%, compared with 7.9% in the US and 79% in Finland.

News of the government’s legal costs was revealed a little over a week after Trudeau used his speech at the UN general assembly to highlight the plight of Canada’s indigenous peoples. For many, Canada’s legacy of colonial relationships had been one of “humiliation, neglect and abuse”, he said.

Trudeau promised his government would do better. “We have been working hard … to correct past injustices and bring about a better quality of life for indigenous peoples in Canada,” he said. “Though this path is uncharted, I am confident that we will reach a place of reconciliation.”