In an official letter, a senior manager from the Children, Youth and Families arm of the Community Services Directorate apologised to the girl for the prolonged detention.

She also apologised for Bimberi staff removing the girl's Indigenous artwork and copies of The Koori Mail from her cell.

The girl launched proceedings in the ACT Supreme Court claiming her human rights were breached and also made a complaint to the Human Rights Commission.

The girl has dropped the lawsuit having received the apology and an assurance from the government that her experience at Bimberi would help inform the treatment of future detainees.

She has since been released from detention.

The girl's lawyer Tom Taylor, of firm McKenna Taylor, said the complaint had been finalised without an admission of liability, but welcomed the response from the government.

"My client's primary concern was ensuring that no other young detainee has to experience what she went through," Mr Taylor said.

"We are pleased that my client's experiences will hopefully bring about change."

Mr Taylor said the government's initial responses to the complaint had been unsatisfactory and confusing.

For instance, the reasons for removing the Indigenous artwork and magazines were because they were "excessive and undermined safety and security".

However the final response acknowledged the particular distress removing the items caused the girl as Mr Taylor said she had used painting as a form of therapy.

The letter, from executive senior branch manager Jodie Robinson, detailed how the girl had been transferred from the Namadgi Unit to the Coree Unit, which is used for incoming prisoners and for segregating detainees.

The girl was isolated for around eight weeks and was separated from the general population, unable to mix with other inmates and participate in programs in the company of others.

Ms Robinson acknowledged the girl was never allowed to put forward a case against her separation or to seek a review as an official segregation direction was never given.

Ms Robinson did not provide any specific reasons why the girl was separated.

She said staff had to take into account a range of factors when assessing whether a detainee should be separated from others. These included, age, gender, sentence status, behaviour in custody and safety.

She admitted there needed to be clarity about the distinction between separation and segregation.

"It can be difficult to apply these general rules in a small facility, where there are limited numbers of young offenders and limited units," Ms Robinson wrote.

"Having reflected on your complaint, we now recognise that a young offender may experience transfer and separation as a form of 'effective segregation'."

Mr Taylor said the Children and Young People Act needed urgent amendments to resolve the conflict between the terms segregation and separation.

"Currently, a young person can be separated, which can satisfy the definition of segregation, and that young detainee has no legal avenue to challenge the decision," he said.

"The ability to separate young detainees whilst in custody is important but only in circumstances where it is justified."

Ms Robinson admitted the reasons for removing the Indigenous cultural items were not communicated to the girl and she said staff had been directed to review policies and procedures relating to personal property.

"I thank you again for your courage in making the complaint you have," Ms Robinson wrote.

"Your experiences will bring about changes that will improve the experiences of present and future detainees at Bimberi."

Mr Taylor added Bimberi staff should receive further training in the application of the Human Rights Act.

"[The act] is not just a document. It should, in a real and genuine way, guide how we treat our most vulnerable," he said.