The family of tragic Louise Furlong said she was "abandoned in her darkest moment" at a mental health facility in Nottingham which was supposed to keep her safe.
They claim "catastrophic failures in care led to the death" of the 19-year-old, who died at Highbury House in Bulwell in September 2022, where she was being treated.
This week the healthcare assistant who was supposed to be observing her - Sylvia Quaye-Mensah - pleaded guilty to neglect in relation to the teenager's death.
The 42-year-old, of Ilkeston, will be sentenced in March.
Following her plea and in a statement released through their lawyers, Harkiran Takhar, medical negligence associate at Lime Solicitors, said: "Yesterday's guilty plea confirms what Louise's family has known all along - catastrophic failures in care led to her death.
"Louise was a vulnerable young woman who trusted a mental health facility to keep her safe. Instead, she was abandoned in her darkest moments.
"This case exposes a shocking breach of duty and a collapse in safeguarding standards. Louise's death was preventable. She deserved protection, compassion and dignity - not neglect.
"This tragedy is not an isolated incident - it reflects a wider crisis in mental health provision across the UK, where chronic staff shortages and unsafe environments continue to put high-risk patients in danger.
"Urgent reform is needed to ensure vulnerable patients are never failed in this way again. No family should ever endure the devastation Louise's loved ones have suffered.
"We are continuing to support Louise's family as they pursue a civil medical negligence claim against Nottinghamshire Healthcare Services NHS Trust."
Ms Furlong died on September 12, 2022, after an incident the previous day at the hospital, with an inquest into her "unnatural" death opening in November 2022.
Quaye-Mensah, an agency healthcare assistant who was on duty at the time of the incident, was later charged by Nottinghamshire Police.
On Tuesday, November 18, she pleaded guilty to a single charge of neglect as a care worker on what was supposed to be the first day of her trial at Nottingham Crown Court.
It means she has admitted she did not carry out the required observations on Ms Furlong when she was employed by a private company and working at Highbury Hospital.
Adjourning sentence on the defendant, of Monsall Avenue, until March 2 and handing her bail, Judge James Sampson said: "I am giving you no indication as to the eventual outcome so do not read anything into me adjourning for the preparation of a pre-sentence report.
"This case is so serious that you must prepare yourself for a custodial sentence."
Ifti Majid, chief executive of Nottinghamshire Healthcare, said: "On behalf of the trust, I once again offer sincere condolences to Louise's family and friends for their loss.
"The safety of our patients and the quality of care we provide is of paramount importance. Sylvia Quaye-Mensah was an agency healthcare support worker at the trust and following Louise's death we immediately cancelled all shifts and informed her employing agency.
"We are unable to comment further while judicial processes are ongoing."
Area coroner Laurinda Bower previously adjourned the inquest into the death back in 2022 so further inquiries could be completed.