The government has announced that after more than five years, the last four refugee children on the island are being moved to the US for resettlement.
It claimed to have been "working quietly" to get children out of detention but most of the 122 kids removed from Nauru in the past six months were evacuated by court order or the threat of legal intervention.
The majority required medical attention.
"The Australian government has fought incredibly hard for those children not to be removed for medical treatment," the Asylum Seeker Resource Centre's Jana Favero said.
"The government has spent, in the last six months, five-hundred thousand dollars going to court to fight people, including many children, getting adequate medical treatment."
Having unsuccessfully fought the removals, Scott Morrison's government was now focussed on defeating a bill that would help refugees detained offshore access adequate medical care.
About 600 male refugees remain in detention on Papua New Guinea's Manus Island while a similar number of men and women are thought to be on Nauru.
"I have no doubt that the timing of the removal of the last children, or promise of removal, is due to political shenanigans," Ms Favero said.
"The government absolutely does not want to be defeated in parliament so they're doing everything they can to try and scuttle the bill going forward next week," she said.
"It's unfortunate they're not just doing it because it's humanity and the right thing to do."
The Urgent Medical Treatment Bill, passed by Australia's senate late last year, was the only way to enshrine a robust process for refugees to be allowed to leave Nauru or Manus Island for medical treatment, the advocate said.
"Because we know that if we left it up to the government, as much as they like to celebrate kids getting off or say that they have effective processes, they don't.
"We've had twelve people die in offshore processing. We've had coroner's reports saying that deaths have been preventable. So we can't take the government at its word."
While the last of the children are finally leaving Nauru, a number of young adults who arrived there as children or unaccompanied minors continue to languish in uncertainty and harsh conditions, Ms Favero said.
"They're no longer considered a minor but they're still on Nauru or Manus and still in a really dire medical and physical condition," she said.
"At the moment in the Asylum Seeker Resource Centre, we're currently case-managing seventy unwell adults, and that ranges from young adults through to elderly people over 60 or 70."
Mr Favero said the centre had a wait list of over 215 other refugees who required some form of medical treatment.
"So the critical medical need is still very real for adults on Manus and Nauru. That's why it's absolutely vital that the bill gets passed next week," she explained.