She told a relative: "I'm dying, but I'm going to come back again in 200 years."
But after a decision that raises profound moral and ethical questions, the judge and the girl's doctors expressed serious misgivings about the process, which did not go entirely according to plan. Her mother spent the last hours of her daughter's life fretting about details of the freezing process, which was "disorganised" and caused "real concern" to hospital staff.
The judge suggested that "proper regulation" of cryonic preservation - which is currently legal but unregulated - should now be considered.
Cryogenic preservation of bodies does not fall under the remit of the Human Tissue Authority, which regulates the freezing of sperm and embryos because it was "not contemplated" when the Human Tissue Act 2004 was passed.
Cryonics UK, the non-profit organisation that prepared the girl's body for transport to the US, agreed with the judge.
A spokesman for the firm said: "We expect that future regulation will help hospitals to know where they stand legally and procedurally. The opportunity to utilise professional medical assistance may increase as we become a recognised and regulated field."
The case can only now be reported because Mr Justice Jackson ruled that nothing could be published until one month after JS's death. He also ruled that her parents' names and other specific details should remain secret.
JS, who lived with her mother in London, was diagnosed with a rare form of cancer last year and by August this year she had been told her illness was terminal and active treatment came to an end.
She began researching cryonic preservation online - a controversial and costly process that involves the freezing of a dead body in the hope that resuscitation and a cure may one day be possible - and decided she wanted to be frozen after her death.
Because she was too young to make a legally recognised will, she had to have the permission of both of her parents to sign up for the process.
When she contacted her father, whom she has not seen since 2008 and who himself has cancer, he said he was opposed to the idea, so JS began legal proceedings through a solicitor to ensure her wishes were followed.
She was too ill to attend court, but wrote: "I think being cryo-preserved gives me a chance to be cured and woken up, even in hundreds of years' time. I don't want to be buried underground.
"I want to live and live longer and I think that in the future they might find a cure for my cancer and wake me up."
On October 6, the judge ordered that JS's mother should have the sole right to decide what happened to her daughter's body, while stressing that he was not making any ruling about the proposed cryonic preservation.
He also granted an injunction preventing the father from attempting to make any arrangements for the disposal of his daughter's body. He said he had been convinced JS was a "bright, intelligent young person" with the capacity to bring the application.
JS's parents could not afford to pay for the cryonic process, which costs from £37,000, but her maternal grandparents raised the money needed for her body to be frozen and taken to a storage facility in America - one of only two countries, along with Russia, that has facilities for storing frozen bodies.
Expressing sympathy with the girl's father, Mr Justice Jackson said: "No other parent has ever been put in his position.
"It is no surprise that this application is the only one of its kind to have come before the courts in this country - and probably anywhere else."
He added: "It may be thought that the events in this case suggest the need for proper regulation of cryonic preservation in this country if it is to happen in the future."
How a family tragedy turned into a landmark court case
As 14-year-old JS lay in hospital, waiting for her terminal cancer to claim her life, she found comfort, and hope, in the idea that science might help her to cheat death.
After spending months online researching the theory of cryonics, the freezing of bodies in the hope that they could one day be brought back to life, JS made up her mind.
"I'm dying, but I'm going to come back again in 200 years," she told one relative.
Her mother agreed that being cryogenically frozen represented a chance to resume her life once science had found a cure for her cancer.
Her father, however, saw cryonics as a lose-lose proposition. The most likely outcome was that it would not work, in which case his daughter's family would have been put through unnecessary distress and expense.
The alternative, however, was potentially worse, as he set out in a statement to a judge who was to decide his daughter's posthumous fate.
"Even if the treatment is successful and she is brought back to life in, let's say, 200 years," he said, "she may not find any relative and she might not remember things.
"She may be left in a desperate situation - given that she is still only 14 years old - and will be in the United States of America [where her body was to be stored]."
The disagreement between mother and father forced JS, who as a minor needed the consent of both parents for the process to be carried out, to seek a court order determining her fate.
The court case which followed not only represented a human and family tragedy, but also shone a light on a little-known and highly controversial industry that describes itself as "an ambulance to the future".
Teetering between science fiction and science fact, cryonics is a leap of faith, relying entirely on future medical advances that may or may not happen.
Its proponents frame it as a choice between "definitely" dying and "maybe" living on.
JS, described by her teachers as caring, happy and friendly, was diagnosed with a rare form of cancer in August 2015, and despite in-patient treatment at a London hospital, she was told her illness was terminal and in August this year her active treatment was stopped.
By then she had already spent months researching cryonics and, according to court papers, "pursued her investigations with determination, even though a number of people have tried to dissuade her".
She chose "the most basic arrangement" offered by an American company, the Cryonics Institute, one of only three companies in the world that stores frozen bodies. In order to get her body to Michigan, where the company is based, she also contacted Cryonics UK, a non-profit volunteer organisation that offers the country's only cryonic preparation service.
'I respect the decisions she is making'
Her parents were far from wealthy, but her maternal grandparents managed to raise the £37,000 that was needed.
There was, however, a problem. JS's father, who had not seen his daughter since 2008, (having applied unsuccessfully through the courts for contact visits) had to be told of her plans and asked to sign parental consent forms. He was reluctant to agree.
He was concerned about the moral and ethical implications of the process, and whether he could be pursued for payments at some point in the future despite living on benefits.
His daughter, with her mother's help, hired a solicitor who applied for the disagreement to be settled by the Family Division of the High Court.
When the case came before Mr Justice Jackson last month, JS's father changed his mind, saying: "I respect the decisions she is making. This is the last and only thing she has asked from me."
But he had one condition: that he could see his daughter's body after she died, to say goodbye to the child he had not seen for eight years.
JS and her mother said no, forcing the judge to settle what he described as "a tragic combination of childhood illness and family conflict".
Mr Justice Jackson said "I fully understand the father's misgivings" and pointed out that the girl's doctors felt "deep unease" about cryonics, making the case "an example of the new questions that science poses to the law".
He granted JS's wishes, having noted that "the prospect of her wishes being followed will reduce her agitation and distress about her impending death".
Cryonics UK, otherwise known as the Human Organ Preservation Research Trust charity, was put on standby and as JS's condition worsened, a team of four volunteers assembled at the hospital.
Meanwhile Mr Justice Jackson visited JS in hospital, at her request, and said he was "moved by the valiant way in which she was facing her predicament".
On October 17, ten days after the judge's visit, JS "died peacefully in the knowledge that her body would be preserved in the way she wished".
However, the judge was sent a note by the hospital which made "unhappy reading", he said.
On the day JS died, "her mother is said to have been pre-occupied with the post-mortem arrangements at the expense of being fully available to JS," said the judge.
"The voluntary organisation is said to have been under-equipped and disorganised, resulting in pressure being placed on the hospital to allow procedures that had not been agreed."
The process involves replacing the blood with an anti-freeze fluid, slowly cooling the body to -70C, and then packing it in dry ice to be transported to a storage facility. Although the preparation of JS's body for cryogenic preservation was completed, "the way in which the process was handled caused real concern to the medical and mortuary staff", the judge said.
About a week after her death, JS's body was packed into a metal crate with around 40kg of dry ice and loaded onto an aeroplane bound for Michigan, where it will be stored in a vat of liquid nitrogen by the Cryonics Institute at its facility in Clinton Township.
The company, which also stores dead pets, makes no excuse for the fact that it can only offer the "hope that future medical technology may be able to someday revive and restore them to full health".
To date, around 350 people have been frozen since the process was invented in the 1960s. Around 20 bodies thawed out and had to be buried after a pioneer company went bust, but the Cryonics Institute and its rival, Arizona-based Alcor, have been storing bodies since the 1970s.
There is no proof that the process of cryo-preservation could ever be reversed.
