Raychel Ferguson, who was nine and from Derry, died at the Royal Belfast Hospital for Sick Children in 2001.
Her death was examined as part of the Hyponatremia Inquiry chaired by Mr Justice John O’Hara KC.
In 2018 it found it was a result of “negligent care”.
In January a new inquest opened but has now been postponed after new evidence came to light.
The inquest was ordered by the attorney general in 2019 and was due to start hearing live evidence on 17 October.
Raychel’s mother Marie said the coroner “had no choice to postpone and everyone involved in the case agreed to the adjournment”.
The nine-year-old died a day after an appendix operation at Altnagelvin Hospital in Derry.
Hyponatraemia is an abnormally low level of sodium in blood and can occur when fluids are given incorrectly.
The Hyponatraemia Inquiry examined the treatment of five children and was one of the longest running public inquiries in the UK.
It was delayed many times as documents linked to Raychel’s case were withheld by health trusts.
Last week it emerged that new documents had come to light as a result of recent investigations by the Nursing and Midwifery Council.
BBC News NI reports that additional information relating to a police investigation has also been drawn to the coroner’s attention.
Marie Ferguson said she welcomed the second inquest into her daughter’s death as it gave the Western Health Trust another opportunity “to tell the truth”.
In January, when the new inquest opened, the Western Trust apologised and said it was sorry to the Ferguson family for the death of Raychel.Her parents have long campaigned to find out the truth about their daughter’s death.
“Not one of the 96 recommendations made by the Hyponatraemia Inquiry have been implemented,” Mrs Ferguson said.
“There has been no meaningful ministerial or Department of Health response.
“Since none of the recommendations have been implemented, Raychel’s inquest takes on a new significance when the court looks at how Raychel died while in the care of the Western Trust.
“We need to make sure that what happened to Raychel and how we as parents were treated never happens again.”
In 2018, the Department of Health put a detailed action plan in place to respond to the 96 recommendations made by the public inquiry.Tags: