The parents of Nóra Quoirin are suing a lawyer over controversial posts she made on Facebook about the disappearance and death of the tragic teenager in Malaysia last year.
Meabh and Sebastien Quoirin have initiated defamation proceedings against retired solicitor Anne Brennan in the High Court in Dublin.
The case relates to a number of unproven theories and statements made by Ms Brennan in posts on the social media site in August last year.
Among other things, Ms Brennan was critical of the procedures adopted by police in Malaysia. Her remarks were rejected by a senior police officer, according to local media reports.
Facebook is a co-defendant in the proceedings, which were filed on Monday.
Nóra's disappearance from her family's cottage at the Dusun eco-resort on August 4 last year sparked a massive search. Her body was discovered on August 13 beside a small stream about 2.5km from the resort.
Although her family believe there was a criminal element to what happened, police have said there was no sign the 15-year-old was abducted or raped.
A preliminary post-mortem examination showed she succumbed to intestinal bleeding due to starvation and stress.
An inquest into her death is due to take place next month.
Denis Barror, the Dublin-based solicitor acting for Nóra's Belfast-born mother Meabh and her French father Sebastien, declined to comment on the proceedings.
Ms Brennan denied defaming the couple and said she was "surprised" they were taking a case.
"I will be defending myself. I don't believe they have a cause of action against me," she told the Irish Independent.
Ms Brennan said that while she wrote "very extreme things" on the social media platform, she believed them to be true.
Facebook declined to comment.
Ms Brennan is a former partner in a Dublin law firm, and specialised in employment and equality law. She retired in 2014 due to an illness.
She confirmed her Facebook account was suspended for 30 days last September but was reinstated and remains active.
The case is the second set of proceedings initiated by the Quoirin family since the tragedy occurred. They are also suing the owner of the resort for alleged negligence.
Confirming details of that case last January, Sankara Nair, a lawyer for Nóra's parents, said the family strongly believed she was abducted as she had mental and physical disabilities and could not have wandered off on her own.
The lawsuit alleges a cottage window was found ajar, with its latch broken, on the morning she disappeared.
It is also claimed the resort gate was left open without any security and there was no surveillance camera except for the reception area.
According to the claim, Nóra had poor motor skills and needed help to walk. Although in her mid-teens, her mental age was about five or six years.
Mr Sankara said the resort was not safe for Nóra and that anybody could have come in and taken her.
In an interview with RTÉ News last December, Meabh and Sebastien Quoirin said they were determined to get truth and justice.
"I think we will seek justice in so far as we can. We have to find peace in our own hearts," said Meabh.
"We will carry Nóra with us forever. She's with us here every day. I talk to her every day. She holds my hand. We hear her. We see her in all that we do at home."