As a matter of fact, Ariana Dumbledore was a key character in the backstory of Harry Potter despite only ever appearing occasionally within pages As a young witch, she was unable to control her magic and following a traumatic incident with some Muggle (non-magical) boys This inadvertently led her to cause an accident that killed her own mother.
Such a tragic mischance left Ariana with guilt and fragmented feelings, unable to break free from her haunted past Her life closed only too soon. In a tragic three-way duel between Albus and Aberforth -her brother's, and one of the most powerful dark wizards out there, Gellert Grindelwald (whom we do not even know he was named by J.K Rowling) Ariana was slain.