Isolt Sayre was a Pure-blood witch, originally from Ireland, who escaped from the home of her cruel aunt, made her way to North America, and founded Ilvermorny School with her family (Pm).
Until the age of five, Isolt lived a very happy life with her parents, who were friendly and helpful to their Muggle neighbors, in the valley of Coomloughra in County Kerry. Things changed suddenly for Isolt when an attack involving a fire killed her parents, and an estranged aunt took the girl to live with her in the next valley called Hag’s Glen. Isolt’s Aunt Gormlaith was a fanatical proponent of Pure-blood supremacy who isolated her niece from her Muggle neighbors and any chance of being led astray, going so far as to deny the girl a chance to attend Hogwarts or own a wand. In her late teens, Isolt managed to run away, taking with her Gormlaith’s wand and Rionach Sayre’s Gordian Knot brooch.
After traveling in disguise across the Atlantic Ocean on the historic ship called the Mayflower, Isolt finally settled in Massachusetts near Mount Greylock. There she formed a close friendship with a Pukwudgie she called William after her own father. The creature committed himself to her service after she saved his life. She also formed a relationship with a Horned Serpent in a nearby creek. Their idyllic life in the woods is disrupted, however, when Isolt decided to care for the orphaned Boot brothers, who were attacked by a Hidebehind, causing Pukwudgie William to leave Isolt and go back to the woods because she was set on healing the boys. As Isolt buried Mr. and Mrs. Boot, Isolt encountered their friend, a Muggle named James Steward, who accidentally injured himself with a wand. Isolt healed James, too, and they fell in love and soon married.
Isolt and James adopted the magical Boot brothers, then commited to educating other young wizards. Soon they were teaching a handful of young Native American witches and wizards, as well. Isolt called the school Ilvermorny, after the cottage in which she was born. Inspired by what Gormlaith told Isolt about Hogwarts, she and her family established four houses and incorporated other attributes of the British Wizarding school. As the school grew, so did Isolt’s family as she and James welcomed twin daughters, Rionach and Martha, whom the parents named after their respective mothers.
While her girls were still little and Chadwick and Webster Boot were teenagers, Gormlaith Gaunt located her niece and attacked Ilvermorny. Gormlaith magically made the stolen wand of Slytherin go dormant, so Isolt was unable to use it. The Boot brothers fought valiantly, but were young and could only delay Gormlaith for so long until she made it to the bedroom where Isolt and James tried to save their baby daughters, who had broken the Sleeping Enchantment with their cries due to the power of Love. When all seemed lost, Isolt cried out the name William (thinking of her father William Sayre), and William the Pukwudgie appeared and saved the day by killing Gormlaith with a poison arrow.
Ilvermorny continued to grow and flourish after Gormlaith’s defeat, and Isolt and her husband James both lived to be over a hundred years old (Pm).
Isolt seems to have had a very close relationship with her father (Pm).
Isolt does not speak Parseltongue, but she claims to understand the Horned Serpent (Pm:Ilvermorny). This is because she is a descendent of Salazar Slytherin through the Gaunt family on her mother's side. Only Gaunt descendents were known to be Parselmouths with the ability to understand snake language and open the Chamber of Secrets at Hogwarts (Pm:Chamber of Secrets).
Isolt is descended from Salazar Slytherin through her mother, who belongs to a branch of the Gaunt family. This makes Isolt distantly related to Voldemort, as Tom Marvolo Riddle's mother was a Gaunt.
Through her father, Isolt is a direct descendent of Morrigan, a famous Irish witch and animagus.
Webster and Chadwick Boot are Isolt's adopted sons, while Rionach and Martha are her daughters by birth.
Skilled at hunting with a wand, healing, and wand making.
Affinity for nature, creatures, and the ability to understand Parseltongue.
Isolt = one of many spellings for Isolde or Iseult, the name of multiple characters in Arthurian legend - the most relevant being Iseult of Ireland, who has a wicked uncle and who first meets the man she falls in love with when healing him (source: Wikipedia).
Sayre = William Sayers is recorded as travelling to Virginia aboard the Bonaventure (source: Bonaventure passenger list), which Gormlaith Gaunt took, disguised as a man and using the name of Isolt's late father, William.
Having Salazar Slytherin's legacy come to America through an Irish witch is interesting, since there are no snakes in Ireland. -BB