Emma Buchanan passed away in Robin House Hospice in Balloch, Stirlingshire, after a lifetime battle with the illness.
The Balfron High School pupil had been in intensive care over the summer, but fought back to celebrate her 15th birthday on November 17.
And sister Jordan revealed how Emma got her wish to be with her family at home ahead of Christmas and before the disease finally took hold.
Jordan, 21, said: “Emma had been in Robin House for eight weeks, but got to come home on the Monday before Christmas and spend the night with us.
“She took unwell at 3pm on Christmas Eve and was taken by ambulance with a police escort back to Robin House.
“She became unconscious, and the family stayed with her, holding her hand and talking to her throughout Christmas Day.”
Jordan stayed with her sister throughout the night, until staff called their parents Tracy and Johnny to join her at Emma’s bedside just before she passed away in the early hours of Boxing Day.
Jordan, from said: “We were with her to the end, and there’s never been a braver soul than Emma.
“One of her dearest wishes was to have the extended family around her on Christmas Day, and there was about 25 of us at her bedside in Robin House.
“It’s hard for Mum and Dad to speak at the moment.
“I’m upset but I’m used to talking about Emma and her condition, and I will be speaking at her funeral.
“I believe it’s what she would have wanted, for us all to keep talking about her and remember everything she was and the good things she brought to our lives.”
Tributes have flooded social media following the teenager’s death.
Mum Tracy posted on Facebook: “Doesn’t seem real that today I not only lost my baby girl but my best friend. I am truly heartbroken. Night night Emma... breathe easy my baby.”
After Jordan took to Twitter to reveal that Emma’s favourite band was The Vamps, she received a number of replies from members of the pop band to send their condolences.
Guitarist James McVey tweeted: “Your sister is beautiful. Really sorry to hear this.”
And the band tweeted the message: “Truly a lovely girl. We are thinking of you and your family.”
Jordan said: “We’re going to have some of Emma’s favourite songs at her funeral, including Wild Heart by The Vamps.”
Friends have taken to Facebook and Twitter to remember their brave pal and pay tribute to her, while giving support to one another.
Selina Ross tweeted: “My year at Balfron (High) are so close. The support everyone is giving is absolutely crazy.”
Kaitlin tweeted: “Angry because you didn’t deserve it, sad because you’re gone and happy because you don’t have to suffer anymore.”
Back in September 2009, Jordan did a charity abseil of the Forth Bridge dressed as Wonder Woman, to raise money for the Cystic Fibrosis Trust.
It was such a success that money continued to pour in five months after the event, earning more than POUNDS 2200.
While more than POUNDS 1000 went to the CF Trust, Jordan used some of the cash to buy items for the children’s ward at Stirling Royal Infirmary, where Emma had received treatment.
And money also went to the Starlight Trust, which helped Emma meet the stars of High School Musical at a premiere in London.
Emma’s funeral service will take place on Wednesday 8th January at 12.30pm at Balfron Church followed by her burial at Balfron Cemetery.