When she was young, Cordelia went to the Shadowhunter Academy. She and John eventually settled in Los Angeles and became good friends with the Blackthorns who lived and ran the Institute in the city.
One day in December 2007, Cordelia and John dropped Emma off at the Los Angeles Institute while they were on their way to investigate a report of demon activity. Later that day, Sebastian Morgenstern and his Endarkened forces attacked the Institute, though Emma was able to escape to Idris with the other children.
Much later, the couple returned to the Institute where the High Warlock of Los Angeles, Malcolm Fade, was stealing the Black Volume of the Dead. Because Fade needed sacrifices for rituals he hoped would revive his lover Annabel Blackthorn, he killed Cordelia and John simply because they happened to be there at the wrong time. The spell failed, and their deaths were for naught.
The Clave were unable to track them for a while until their bodies washed up on the beach in Marina del Rey the next morning. Their bodies were disfigured—their skins covered in scars and strange markings, appeared gray, and crumbled away when attempts to move them were made. With no way to transport the corpses, they were burned on the beach and given as close to proper Shadowhunter funeral rites as they could.
Because of the Dark War, their deaths were dismissed as casualties. Their young daughter wanted to confirm for herself and stole their case report from Consul Jia Penhallow's desk. She examined the circumstances further and became convinced that their deaths were caused by something else entirely.
Because she had been orphaned, Emma was offered a place at the Shadowhunter Academy. She refused, wanting to return to Los Angeles so she could investigate their deaths. She became parabatai with her best friend Julian Blackthorn, and she has since lived with the Blackthorns as a ward of the Institute.
Emma spent the next five years investigating their deaths to figure out the real cause herself. After Malcolm began killing faeries and other mundanes the way Cordelia and John were killed, Emma was eventually able to discover the truth and went on to get justice, and vengeance, by killing Malcolm herself.
- Though unrelated, Cordelia shares a name with Cordelia Carstairs from the early 1900s. Cordelia was also given as her daughter's middle name.