Inspirational Margot celebrates her second birthday today.
Her parents Vicki and Yaser said they were told Margot's chances were 'less than one per cent' and that they had overridden the instinct to fight against such small odds.
Margot was diagnosed with both acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML) last year.
Her fight against the disease has captured the hearts of people across the country, with 17,000 people now getting updates on the Team Margot Facebook page.
Earlier this month she was given experimental medication at Sheffield Children's Hospital in a bid to bring the ALL clone into remission.
But a bone marrow aspirate revealed both diseases were still present, leading the youngster's family to make the most difficult of decisions not to pursue any other forms of treatment.
The family had considered other therapy options with specialists in America, but decided against it after medical experts told them the chances of Margot being able to lead a normal life after subsequent treatment was slim.
Father Yaser wrote an emotional post on the Facebook page, outlining the impossible decision he and Vicki, who are originally from Essington, have made.
He said: "Vicki and I made a decision last night, after a long conference call with my two cousins, both cancer doctors and one of them a specialist transplant physician.
"They endorse the advice we have already received from Great Ormond Street Hospital and tell us that having followed Margot's journey closely since diagnosis, the care Margot has received has been flawless.
"The real clincher was when we asked what the likely odds are of Margot going for the Phase I DOT1-L treatment in New York, coming through that and then having the subsequent necessary treatments that enable her to have and lead a 'normal life'."
Yaser said his cousin put the situation into context when he told him that 'factoring it all in ... I would say Margot's chances are less than one per cent. It's not zero, but it's under one per cent'.
Yaser added: "We want the best quality of life for Margot with what little time we have left. So we have made that decision overruling the instinct to fight against slim odds.
"We don't want her to suffer unnecessarily, least of all for our own sake to somehow make us or others feel better.
"We also need to tend to and care for the rest of the family, so are now working towards making a proper plan to ensure we are best equipped to deal with issues arising with the boys.
"Thank you for your support and well wishes."
Margot, who has two brothers Oscar and Rufus, was diagnosed with an extremely rare form of leukaemia last October.
A Swab4Margot campaign, backed by celebrities such as Stephen Fry and John Bishop, led to more than 50,000 people requesting swab kits from charity Delete Blood Cancer UK.
Eventually a match was discovered and the operation was deemed a success.
Doctors said they thought Margot was 99 per cent certain to be disease free following tests in March, however tests in June showed traces of the disease had returned.
The family's hope it was a slight set-back were dashed last month when they revealed the disease had progressed from a one per cent presence to somewhere between 60 and 80 per cent.
A short video of the youngster was posted on the Facebook page last month, in which she repeated her father's words 'just one more' to support a campaign being run by blood cancer charity and bone marrow register Anthony Nolan.