Hila Tacorien, the individual who manifested as the Caliburn Ghast or the Witch of the Well, was a human time traveller and, reportedly, the great-great-great-great-great-granddaughter of Emma Grayling and Alec Palmer.
At one point, she accidentally landed, and got trapped in a pocket universe with the Crooked Man. While she was only there for around five minutes from her perspective, her presence in N-Space was felt from the beginning to the end of the planet Earth.
Hila was finally saved when the Eleventh Doctor, through the power of Emma Grayling, entered the pocket universe to retrieve her. She crossed through the wormhole and arrived at the Caliburn House in 1974. According to The Doctor, her status as a pioneer explorer of time made her a fixed point in time, thereby preventing her from being returned to her own time; however, he soon revealed to her that Emma and Alec were her ancestors. (Hide)
Manifestation as the Caliburn Ghast
Within N-Space, she manifested as the ghost that haunted the Caliburn House. Over the years, she was given many names: the Wraith of the Lady, the Maiden in the Dark, the Witch of the Well and the Caliburn Ghast. According to Professor Alec Palmer, she was mentioned in local Saxon poetry, and parish folk tales.
In the 17th century, a local clergyman saw her, and wrote that “her presence was accompanied by a dreadful knocking as if the Devil himself demanded entry.” During World War II, American airmen stationed at the house left “offerings of tin Spam.” The tins were found in 1965, bricked up in the servants pantry, along with “a number of hand written notes, appeals, to the ghost: ‘for the love of god, stop screaming.'”
She was called “the Witch of the Well”, due to a wormhole which opened at Caliburn House.