Gormlaith Gaunt is Isolt Sayre’s aunt and kidnapper, who is killed in her attack on Ilvermorny School of Witchcraft and Wizardry.
Gormlaith Gaunt was a fanatic about blood purity, and she disapproved of her niece being raised to have an open and positive attitude toward Muggles. Determined to to prevent Isolt from ever sullying the family bloodline by marrying someone other than a pureblood wizard, Gormlaith killed Isolt’s parents in a fiery attack on their home and took the five-year-old girl to live an isolated life back at her home in Hag’s Glen. Dedicated to indoctrinating Isolt, Gormlaith barred the girl from going to Hogwarts or owning a wand and forced her to observe her aunt put jinxes and curses on Muggles and animals.
For twelve years, Gormlaith used Dark Magic to force Isolt’s obedience and compliance. But then Isolt absconded with her aunt’s wand and left Ireland on board the Mayflower in 1620. More than a decade later, word got around the Irish wizarding community that a Wizarding school had been established in the New World. Gormlaith learned that the headmistress, who was married to a Muggle, is nicknamed Morrigan, but she remains skeptical that it could be Isolt until she discovered that the American school shared its name with the Sayres’ cottage in Coomloughra. Outraged, Gormlaith set out to capture her great-niece and bring them back to Ireland to carry on the bloodline. She disguised herself as a man and used her late brother-in-law’s name, William Sayre, while crossing the Atlantic aboard the Bonaventure.
Gormlaith made her way to Ilvermorny, where she put Isolt and her husband into a magical sleep and deactivated the stolen wand before launching an attack. She battled Chadwick and Webster Boot, using Dark Magic but not wanting to kill them in case they were Pure-blood. In the end she was killed by a poison arrow to the heart from William the Pukwudgie. She screamed, desperately trying to find a way to save herself, then broke into countless brittle pieces (Pm:Ilvermorny).
Gormlaith attended Hogwarts in her youth. She later told Isolt stories about it in an (unsuccessful) attempt to turn her off from the school (Pm).
When the Boot brothers wanted to go to Hogwarts, Isolt did not explain that Gormlaith was a danger to them all because she did not want to frighten them. However, Chadwick overheard his parents discussing the old witch and became afraid of her anyway (Pm).
Gormlaith Gaunt was an Irish descendant of Salazar Slytherin. She was from the the same family as the English Gaunts, whose line eventually produced Tom Marvolo Riddle.
She was estranged from her sister Rionach Sayre and, by proxy, her brother-in-law William Sayre. The Sayres' daughter Isolt was Gormlaith's niece.
Dark magic, curses and jinxes, tracking, dueling, Parseltongue
Gormlaith was the name of the wife of the famous Irish King Brian Boru. In literary works, this Gormlaith is consistently presented as evil (source: Wikipedia).
The real-life passenger list for the Bonaventure includes a person called "William Sayers".
The idea of a Parseltongue and descendent of Slytherin living in Ireland is interesting, as Ireland famously has no snakes. -BB