A teenage Harry Potter fan who survived a shooting massacre that killed her family has received a handwritten letter from JK Rowling.

Cassidy Stay, 15, from Houston, Texas, was grazed by a bullet and suffered a fractured skull during the July attack on her family. She pretended to be dead as the gunman continued his rampage and then called police to raise the alarm that he was also planning to target her grandparents.

Cassidy, left, pictured with her mother Katie, 34, father Stephen, 39, and siblings Emily, nine, Rebecca, seven, four-year-old Zach and Bryan, 14

Just three days after the murders of her parents and four younger siblings, the brave youngster addressed a memorial for her family, quoting from Harry Potter's Hogwarts' headmaster Albus Dumbledore.

"Happiness can be found even in the darkest times if one only remembers to turn on the light," she told mourners. "I know that my mom, dad, Bryan, Emily, Becca, and Zach are in a much better place and that I'll be able to see them again one day. Stay strong."

JK Rowling was so moved by the courageous 15-year-old, she sent her a letter of comfort, handwritten in purple ink, from "Dumbledore," accompanied by an acceptance letter to Hogwarts, a list of school supplies and a signed book, The Telegraph reported.

The author's rep told the newspaper: “We can confirm that JK Rowling was in touch with Cassidy Stay, however, the contents of the letter remain private.”

Ronald Haskell, 33, the former brother-in-law of Cassidy's mother, has been charged with capital murder and could face the death penalty if he is convicted.