“Loving daughter and granddaughter” Amanda Selby, 15, was killed by her brother in July.
A 19-year-old has admitted killing his teenage sister in a caravan on the north Wales coast.
Amanda Selby, 15, died at the Ty Mawr Holiday Park in Towyn near Abergele, Conwy county, on 31 July.
Matthew Selby, of Windermere Crescent, Ashton-under-Lyne, appeared at Mold Crown Court to enter his plea.
He was due to stand trial for murder this month, but has now pleaded guilty to manslaughter on the grounds of diminished responsibility.
The case has been adjourned until 18 March when sentencing will take place.
Selby appeared via videolink from HMP Berwyn, near Wrexham, for the hearing, which lasted less than 10 minutes.
Ian Unsworth QC, prosecuting, said the Crown accepted the plea to manslaughter, based on close analysis of psychiatric reports.
Judge Rhys Rowlands said: “I too have read the reports from both psychiatrists and plainly I understand the decision taken by the Crown.”
Gordon Cole QC, defending, said Selby would be seen again by a psychiatrist before his sentencing.
At an inquest opening, Amanda’s provisional cause of death was given as asphyxia as a result of neck compression and external airway obstruction and crush asphyxia.
In a tribute, Amanda’s family said: “Amanda was a loving daughter and granddaughter – she was caring, thoughtful, liked to help others and very much loved.”
Amanda’s school, Droylsden Academy in Manchester, said: “Our school family is devastated by this awful news.
“Amanda was a lovely student and she will be sorely missed by students and staff.”
Jiu Jitsu club Kamiza Dojo said Amanda and her mother had been a big part of the club for many years.
It said: “Our club is saddened to hear the tragic news that one of our students, Amanda Selby, has lost her life while on holiday with her family.
“The Kamiza Dojo family is truly devastated by this awful news. We are truly heartbroken, Amanda will be sorely missed.”
Police were initially called to the caravan park after reports of a “domestic disturbance”.