Gwenllian ap Glyn Dŵr
Half tree-light/half human
Gwenllian was born out of wedlock to an old tree-light and the prince of Powys, Owain Glyn Dŵr (Glendower). She did not approve of her father's poet and adviser, as she believed that he was feeding her father lies and manipulating him, so she tried to stab him at dinner one night. This led to her being used as the bait in Glendower's false grave, set up in the cave in Cabeswater to distract from the real grave of Owen Glendower in Virginia.
When Gwenllian was put into the grave, her hands and feet were bound and she was placed in the coffin facedown, a burial style seen in suicides, adulterers, and witches of the time. She was "put to sleep", but she never actually slept. Instead, she stayed awake for six hundred years until she was found by Blue, Gansey, Ronan, and Adam. They brought Gwenllian out of the cave and back to 300 Fox Way with them.
Gwenllian describes herself as a "mirror" and a witch. This means that she can amplify and reflect magic and energy off of herself, very similarly to Blue's abilities. She has an affinity for singing, whispering, and shrieking instead of talking.