Petrah is described as beautiful, tall and thin like her mother with freckled skin as pale as Manon's and braided golden hair - a deep, brassy color. She is beautiful, like so many of the witches, but calm and grave. As the heir to the Blueblood Clan, above her deep blue eyes, she wears a worn leather band in lieu of the iron-star crown. In Empire of Storms, she is seen wearing a cloak of midnight blue.
As an Ironteeth witch and heir to her Clan Petrah is ruthless and cunning as seen during the War Games however unlike most Ironteeth witches, Petrah is grave and calm, described as always having been odd, living with her head in the clouds. While both Manon Blackbeak and Iskra Yellowlegs could be called cruel and heartless, Petrah seems to be the opposite, even visibly flinching as she watched Titus attack Abraxos. She expressed interest in allying herself with Manon.
Petrah came to the Omega site with the rest of the Blueblood witches claiming the uppermost chambers for themselves.
Petrah showed interest in the wyvern Titus as had the other heirs however when it came time to choose she chose a large female named Keelie. Petrah and Keelie were very close as mount and rider, so close that Petrah approached Manon claiming that Keelie had expressed the desire to share meat with Abraxos. When Manon claimed that the wyverns don’t talk, Petrah simply replied, “Don’t they?”
During the War Games, while the Blackbeak and Yellowlegs witches were engaged in battle, Petrah appeared above aiming to steal the egg while they were distracted only to be caught by Iskra’s bull. The two heirs and their wyverns were locked in battle until Iskra’s bull at the witches command clamped its jaw down on Keelie’s neck leaving the witch and wyvern to plunge to the ground.
Seeing the still living Blueblood heir falling to the ground Manon and Abraxos swooped down, Abraxos was too small to save Keelie but they could save Petrah. Manon realized that Petrah had passed out from the lack of air but Keelie was fighting to twist herself and save the witch on her back. Manon leapt from her wyvern to Keelie, cut Petrah from her saddle and saved the life of the Blueblood heir.
The next day Petrah would not rise from her bed, rumours circulated that she had been broken in her soul when Keelie died.
Petrah is present at Manon’s trial for the killing of Zelta Yellowlegs where she requested the right to question Manon. She asked Manon if she considered her a rival and if so why she saved her life during the war games. Manon admitted that after seeing how hard Keelie fought to save her rider, Manon could not let her death be in vain, Petrah was touched that Manon had remembered the wyvern's name. Petrah spoke in support of Manon, arguing that Manon had save a rivals life once before why would she do that only to kill another.
During the fight between Manon and the Blackbeak Matron, Petrah prevented her mother from interfering.