Millie Rose Heaton had been diagnosed with neuroblastoma and had been battling the illness.
Her parents Lynsey and Michael were recently told the cancer had spread.
They had raised more than £200,000 to take their daughter to Germany for treatment.
But her condition deteriorated in the last few days and she died at 7.15pm on Wednesday.
Exactly 24 hours later hundreds gathered near her home in Skelmersdale to release balloons in Millie's memory.
Thousands of messages have been left on the Millie Rose Appeal Facebook page https://www.facebook.com/MillieRoseAppeal after her family posted that she had 'gained her angel wings...surrounded by the people who love her most'.