Cheryl McKeown collapsed outside court on Monday as her elderly parents were acquitted of her 14-year-old daughter's manslaughter.

But she says the family is now living with the agony of not knowing what happened to Rebecca, who she described as "the light of our lives".

"We have lost Rebecca and Rebecca's daddy and we have lost the opportunity of family life," Mrs McKeown told UTV.

"We have lost all the hope and joys of our family's achievements. I have lost myself. This is only half a life that I now lead and I can only keep going for the sake of my children."

Life as everyone else experiences it has been ripped apart and there is no prospect of repair now.

Cheryl McKeown

David and Sarah Johnston - aged 88 and 86 - left court completely exonerated of all charges relating to the death of their profoundly disabled granddaughter.

The trial ended in dramatic circumstances when judge Mr Justice McLaughlin directed the Crown Court jury to acquit the elderly couple.

Rebecca died five days after sustaining an injury thought to have been the result of a sexual assault, which the Crown claimed had happened while she was in the care of her grandparents.

But prosecuting QC Toby Hedworth said, having "anxiously" reviewed the state of the evidence and testimony which was yet to come, a decision had been made to offer no further evidence against Mr and Mrs Johnston.

He explained it was the evidence of Dr Mary Donnelly and of State Pathologist Professor Jack Crane that had led the Crown to their decision.

During the trial, the doctor had admitted that her examination of the young girl may have unintentionally caused the internal injury.

Professor Crane had, during his testimony, said he could not be sure that the laceration had led to the Pneumonia that tragically killed the teenager.

Mrs McKeown continued: "For eleven years chaos has abounded where reason has failed to provide any answers. We are also now back to the 19th March 2011.

"This was the day something terrible happened to our beautiful Rebecca."

I was Rebecca's lifeline but she was the light of our lives.

Cheryl McKeown

"Rebecca lost her life because of what happened that night and our lives stopped that day as well."

Mrs McKeown said Rebecca achieved so much in her short life, raising £175,000 for the Children's Hospice to be built - but never had the opportunity to see it for herself.

"We are thankful that Rebecca's life has allowed other children with special needs to be cared for in a peaceful and beautiful place.

"We hope that Rebecca is at peace."

In a statement, the Public Prosecution Service said that, while it acknowledges the level of public interest in the reasons why it was necessary to discontinue the prosecution of David and Sarah Johnston, certain aspects of the case remain under consideration and in such circumstances it would be inappropriate to comment further.

"The decision to prosecute was based on a full and careful analysis by the PPS of the available evidence which included circumstantial, forensic and medical evidence," it said.

"During the course of the prosecution the evidence changed to such an extent that the PPS concluded that there was no longer a reasonable prospect of conviction and accordingly discontinued proceedings. The decision was taken at the earliest possible opportunity after the evidential issues came to light."