After the reopening of the Scholomance at the end of the Dark War, Amelia was one of the Shadowhunters who attended the school and became a Centurion. Along with many of her colleagues, she was invited by her friend and fellow Centurion Zara, with whom she shared beliefs about Downworlders, to join the Cohort, a group led by Zara's father, Horace Dearborn.
In 2012, Amelia attended the funeral of Livvy Blackthorn and Robert Lightwood where she was seen giggling with her friends. She was among the Cohort members guarding the house where Emma Carstairs and Julian Blackthorn were supposed to be staying, preventing anyone from finding out that they weren't there. When Diana Wrayburn was trying to force her way into the house, Amelia and Vanessa Ashdown stopped her, and Amelia wasn't threatened when Consul Jia Penhallow arrived.
Later, under Zara's command, she was part of the group that followed Diana and Jia to Brocelind Forest where they caught them talking with Gwyn ap Nudd, the leader of the Wild Hunt, and imprisoned them for consorting with faeries.
Shortly after, Amelia, among the group led by Manuel Casales, went to the camp of some members of Livia's Watch in the Brocelind to kill Jace Herondale and Clary Fairchild. They were ambushed and caught by the Shadowhunters staying at the camp and the Downworlders waiting and hidden amongst the trees and were taken to the Imperishable Fields. There, she participated in the battle that unfolded during the staged parley arranged by Horace and King Oban and fought alongside the Cohort and the Unseelie faeries against Downworlders and her fellow Shadowhunters. The Cohort lost the battle and Amelia, along with all the members who took part in the fight, was taken prisoner to the Gard where she was tested by the Mortal Sword and confessed her crimes.
During the meeting in the Council Hall, Jia granted her and all the Cohort members a lenient punishment and gave her a chance to rejoin the Clave, each member was to be sent to an Institute away from the other members, where they would be given a chance to redeem themselves before returning to Alicante.
She was also entitled the right to vote for the Clave's new Consul when Jia stepped down, but when Alec Lightwood was elected, she and her friends refused to recognize him as Consul and threatened to commit mass suicide by cutting their throats if the non-supporters of the Cohort didn't leave Idris permanently. At Zara's signal, Amelia sacrificed herself for the cause, stabbing herself in the stomach with a dagger to prove they weren't bluffing. No one from the Cohort or the Council moved to help her and she bled out on the floor of the dais. Emma Carstairs thought her death was too cruel, for she died unmourned and for a cause that didn't care about her.
- Queen of Air and Darkness (first and only appearance)