Grianne Ohmsford, also known as the Ilse Witch, is a character in The Voyage of the Jerle Shannara trilogy, the High Druid of Shannara trilogy, and The Dark Legacy of Shannara trilogy. She goes through many difficulties and extreme situations throughout her life, starting with the death of her parents at the hands of the Morgawr and moving on to her time as the Ilse Witch, her career as Ard Rhys of the third Druid Order, and her times spent trapped in the Forbidding.
Grianne Ohmsford was abducted from her burning home when she was a young child by a powerful and evil warlock called the Morgawr, who knew that the power of the wishsong held by the Ohmsford family had the potential to destroy him. He brainwashed Grianne into believing that it was the Druid Walker Boh who had destroyed her home and killed her family. Taking her as his pupil, he taught her the dark arts, which along with the power of the wishsong made her a very powerful witch. Taking on the name of the Ilse Witch, she constantly sought to find and destroy Walker Boh for bringing such pain to her life. She also secretly plotted for the day she would destroy the Morgawr.
The Ilse Witch followed Walker to Castledown in Parkasia, but there she met her brother Bek Ohmsford, whom she had believed dead since having hidden him in a cellar while their home was being attacked and their parents were killed. Bek used the power of the Sword of Shannara to reveal the truth about her past to Grianne. Later, when Walker was mortally injured destroying the malicious artificial intelligence called Antrax, he named Grianne as his successor as last of the Druids before dying, and on her return to the Four Lands she established the third Druid Order, becoming its Ard Rhys.
Twenty years later, Grianne would again find herself menaced, this time by treacherous Druids within the order. She ends up trapped inside the Forbidding and at the mercy of the Demons trapped within. It would be up to her nephew, Pen Ohmsford, to save her from the Forbidding and the Straken Lord Tael Riverine.
After returning from the Forbidding and helping Pen send a Demon called the Moric back into the Forbidding, Grianne retires as Ard Rhys, knowing the Druid Order cannot survive with a person as divisive as her at its head. Despite the troubled nature of Grianne's term as Ard Rhys, she had managed to forge an alliance between the Druids and the Trolls, and in her final act as Ard Rhys, she negotiates a treaty that forbids the use of diapson crystal weapons in the Four Lands.
After retiring, Grianne traveled with Pen to try to save Pen's girlfriend Cinnaminson, who was transformed into an aeriad spirit in service to the Tanequil, a magical tree. Grianne is able to free Cinnaminson, but only by taking the Rover girl's place as an aeriad. As a spirit, she lives unfettered by both her guilt over her history as the Ilse Witch and her fear of the evil reawakening in her, and she finds freedom.
However, over a century later Railing Ohmsford, a descendant of the Ohmsford family, sets out to find and release Grianne from the Tanequil so that she might save his twin brother Redden, who had become lost in the Forbidding and captured by Tael Riverine. After Pen had rescued Grianne from the Forbidding over a century earlier, Tael Riverine had become obsessed with the idea of finding Grianne again and making her his wife, and Railing was hoping the Straken Lord's obsession meant that Grianne's return would prove to be key to saving his brother.
Railing eventually succeeds in reaching the Tanequil, where Grianne's aeriad spirit greets him and tells him she cannot help. Unwilling to give up, Railing speaks to the Tanequil instead, and at his insistence the tree eventually releases Grianne. However, she is not returned whole, but as the malevolent Ilse Witch.
The Ilse Witch, while resentful of what Railing has done to her, has no desire to return to the Tanequil. She forces Railing and the crew of Rovers piloting his airship to take her to where the Straken Lord's army, freed from the Forbidding by the dying of the Ellcrys, have begun their invasion of the Elven nation in the Westland. Along the way, she reveals to Railing that she intends to take Tael Riverine's place as ruler of the Demons, horrifying him.
When the airship reaches the armies, the Ilse Witch confronts the Straken Lord and proceeds to do battle with him while Railing, Mirai Leah, the Demons, and the Elven army watch. She easily tricks the Straken Lord and traps him with his own conjure collar, and having rendered him helpless, she kills him with his own scepter. With her victory, the Demons acknowledge her as their new leader.
With the Straken Lord defeated, the Ilse Witch turns on Railing. However, Redden Ohmsford, who had managed to free himself from the Forbidding and reunite with Railing during the Ilse Witch's duel, uses a combination of the wishsong and the crimson Elfstones, which he had brought out of the Forbidding, in a desperate attempt to stop her. Although the magic of the wishsong and the Elfstones initially overpowers her, she recovers and begins to fight back.
The twin brothers are in imminent danger of being killed by the witch when Arlingfant Elessedil restores the Ellcrys and the Forbidding. Because the Ilse Witch had made herself one of the Demons, she disappears with all the other Demons when they are banished back into the Forbidding.