In 1873, a twelve-year-old Will opened a Pyxis out of curiosity. A demon named Marbas came out and was about to attack Will when Ella stepped in front of him and tried to fight Marbas with a seraph blade she did not know how to use. Before the demon fled, Marbas stung her with his poison and threatened Will that all those he loved and those who loved him would be destroyed, beginning with Ella. She immediately went to comfort her brother and consoled him, assuring Will that the demon's threats were empty. While her brother went to bed early, she told her parents that she was feeling ill.
Ella died that night, her body swollen and unrecognizable. Will fled his home, believing that the demon Marbas's curse had taken effect and that everyone close to him were condemned to death. It was later discovered that she was in fact killed by Marbas' demon poison, and not Will's curse.
Ella was the kind of sister who would have done anything for her siblings. She always looked after them and was also apparently very motherly. However, she was not as openly affectionate as Cecily, so it was considered a big deal whenever she made a loving gesture. Ella also had the bitter sense of humor that ran in the Herondale bloodline. She was very brave, almost fearless; she would stand up to anything to protect her siblings.
Despite her lack of training, the Shadowhunter blood in her seemed to run strong, able to hold herself in the face of danger and was able to wield a seraph blade in battle against a demon, though not as effectively as she would have had she been trained.
- Clockwork Prince (first mention)
- Clockwork Prince: Manga (mentioned only)
- Clockwork Princess (mentioned only)
- Clockwork Princess: Manga (mentioned only)
- Nothing but Shadows (mentioned only)
- Her character was originally named Emma before Cassandra Clare changed it to avoid confusion with a previously-mentioned Emma in the series.