Quite who cast the spell that killed Ariana was unclear, although when Harry met Albus Dumbledore in King's Cross after he was nearly killed during the Battle of Hogwarts, the old headmaster strongly hinted that it was Grindelwald who shot the mortal curse.
Ariana died when she was accidentally struck by a curse in a three-way duel between her older brothers and Dark Wizard Gellert Grindelwald, Albus's friend at the time; it was never known who struck the killing blow. This event would have a profound impact on both her brothers' lives.
She was the younger sister of Albus and Aberforth Dumbledore. At the age of six, Ariana was attacked by Muggle boys who saw her practising underage magic, which left her traumatised to the point of rendering her magical abilities uncontrollable. Ariana would later become an Obscurial as a result.
The specifics of the attack are unknown. I don't think sexual assault is likely from Aberforth's description. My best guess is the boys shook her and shoved her around, as they tried to make her show them the trick. For a child of six, the terror was probably worse than the physical trauma.
But Ariana is not a Squib. The narrative treats her as a Squib in order to allow Harry to draw the uneasy parallel of wondering whether Ariana was treated in a way reverse to his treatment by the Dursleys — shut away because of her lack of magic, while he was shut away because he had it.
Though nominally a Muggle-born witch, Hermione is descended from the Dagworth-Granger family through her father's squib heritage.
The term "Squib" is only used in the Harry Potter films once and is never really explained, but it is an interesting phenomenon in the series nonetheless. It is also imperative to define because Squibs can play an important role in the Wizarding World.
Dumbledore escapes, dramatically, and Umbridge is appointed Headmistress, although she is never able to get into the Headmaster's office after Dumbledore's departure. Marietta Edgecombe's defection not only betrayed Dumbledore's Army, but ultimately doomed Harry and Cho Chang's relationship.
What caused his hand to turn black and decay? Like all the other Horcruxes Voldemort created, a protective curse was placed over the Ressurection-Stone-turned-Horcrux. Anyone who tried to take the ring would be cursed the moment it touched their finger, which is exactly what happened to Dumbledore.
In book 7 we all go through the betrayal as Harry finds out that beloved Dumbledore raised Harry to be killed. We find out that he hid information and manipulated people all his life, and is very much on an ethically grey area.
Ariana Dumbledore was raped. The nature of Ariana's attack is left deliberately ambiguous. If what happened had been anything besides rape, it would have been described or at least directly stated.
Ariana wasn't a squib though, she sounds more like an Obscurial - the same as Credence. At 14-years-old, Ariana flew into a rage and her magical outburst killed Kendra. "Then, when she was fourteen ... see, I wasn't there," said Aberforth.
Following Lord Voldemort's defeat at the hands of her student Harry Potter and the deaths of Headmasters Albus Dumbledore and Severus Snape, McGonagall takes the position of Headmistress.
Ariana Dumbledore was the sister of Albus and Aberforth Dumbledore. She died quite young, at approximately 14 years of age.
In the sequel, she decides to join Gellert Grindelwald in his crusade on the promise that she can marry Jacob due to a law refusing to allow humans and witches to marry. However, Queenie turns to the side of good again and both she and Jacob marry each other in 1932.
She seemed to know what everyone else in the Order knew about Snape's allegiances, but no more, since she'd stopped believing he was on their side after Dumbledore's death.
Wanting to use it to revive his family and apologise for his selfishness in the past, Dumbledore lost his common sense, forget that it was a Horcrux which may have been cursed, and adorned it on his right hand. Almost immediately, the curse triggered, and nearly killed Dumbledore.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
After Dumbledore returned to Hogwarts, he used Godric Gryffindor's Sword to crack the Resurrection Stone so as to destroy it as a Horcrux. While the act did destroy the ring as one of Riddle's Horcruxes, it did not stop the fatal curse. The curse gave Dumbledore's hand a withered black look, as though it had died.
Dumbledore also gives Harry the Resurrection Stone.
"To Harry James Potter, I leave the Snitch he caught in his first Quidditch match at Hogwarts, as a reminder of the rewards of perseverance and skill," his will reads. For a while, Harry is unable to open the snitch.
However, her name has attracted some controversy in recent years. Unlike other strong female characters, whose names are not only real but have deep literary and cultural references, Cho Chang's name only contains a vague indication of her Asian origin. Many have pointed out that "Cho" might be a Korean surname.
Harry describes Umbridge to Sirius Black, saying that she's vile enough to be a Death Eater, despite not being one. Umbridge is also depicted to be a prejudiced person, despising half-breeds and Muggle-born witches and wizards to the point of firing Hagrid due to his half-giant birth status.
The fan asked the author if Aunt Petunia was a Squib (a non-magical person who is born to at least one magical parent) and Rowling replied: "Good question. No, she is not, she is not a Squib. She is a Muggle.
(n) a person who decides for spurious or selfish reasons not to honor an undertaking (to take part). (v) to withdraw from an undertaking: "That person is a squib".
They aren't quite Muggles
As Ron explains to Harry, 'They're kind of the opposite of Muggle-born wizards,' and are often the odd-one-out in one way or the other.