"It is with the heaviest of hearts and the greatest of love that we share the news that our daughter Gabriella passed away last night," the statement said. "Thank you for loving our daughter and for all of your support."
Gabriella, who was diagnosed almost a year ago with brain cancer, began hospice care at home last week due to a sudden decline in her health, said Chris Croll, a close friend and spokesperson for the Miller family.
"Everybody had an opportunity to say their goodbyes and their final words, and she passed very peacefully," Croll said.
Gabriella first drew national attention last year through a letter-writing campaign that helped raise more than $275,000 for the Make-A-Wish Foundation. She submitted her own request for a dream trip to Paris, which she took with her family in May soon after she was diagnosed in November 2012. But the philanthropic student also wanted to make sure that other children would have their wishes granted, her mother, Ellyn Miller, said at the time.
"She was always thinking about other kids," Miller said. For years before Gabriella's own diagnosis, she had donated her long, dark hair to Locks of Love, a group that provides hairpieces to children suffering medical hair loss.
The Miller family learned that the Make-A-Wish Foundation would secure a $1 million donation from Macy's if the company received 1 million letters to Santa Claus before Christmas. So they decided to start a letter-writing campaign, titled "Make A Wish with Gabriella," and tens of thousands of letters streamed in first from the local community and the Washington region, then from across the nation, then from across the world.
Gabriella delivered nearly 241,000 letters to her local Macy's store days before Christmas last year. Letters sent in separately on her behalf brought the total to more than 250,000, Ellyn Miller said.
In May, Gabriella was named Loudoun County's Volunteer of the Year for her work. Before a standing ovation in the county boardroom, she shared her optimistic philosophy with the crowd: "You might have a bad day today, but there's always a bright star to look forward to tomorrow," she said.
The success of her letter-writing campaign only strengthened Gabriella's ambition to help her cause. Along with her family, she decided that she wanted to do more to help raise the public's awareness of the need for pediatric cancer research.
This year, the Millers launched the Smashing Walnuts Foundation, named for a unique family ritual: when Gabriella was first told that her brain tumor was about the size of a walnut, she and her family decided to use frying pans to smash walnuts on the rails of their deck to help the young cancer patient visualize defeating her illness.