On the trip that changed their lives, Abigail was on her way to Constantinople, with her two companions, to join and marry her fiancé, whom Jonathan was said to be unhappy about. According to the Shadowhunter's Codex, the three of them were attacked by a swarm of demons at Lake Lyn and were eventually overpowered. After Jonathan had successfully called for the Angel Raziel and received the Mortal Instruments in which to create the Nephilim, his first order of business was to nurse Abigail and David back to health, and to have them both drink water from the Mortal Cup, in order to make them Nephilim as well.
In her time as a Shadowhunter, Abigail demonstrated that the female Shadowhunters were no less fierce and resolute than the men who were organized under Jonathan’s banner. When she grew older, and could no longer physically wage war against demonkind as she once had as a warrior, she turned to the esoteric knowledge of the Gray Book and the study of adamas. During this process, she became the first Iron Sister. Along with six other Shadowhunters, she constructed the first adamas forge, which was the earliest incarnation of the Adamant Citadel, where Iron Sisters craft the weapons of the Nephilim. When the Adamant Citadel was built, it was decided that the place itself, along with the Iron Sisters who resided there, would only be open to female Shadowhunters, in a way to protect the citadel from unwanted interference by male Shadowhunters.