Ilsa was "born" from the bombing of the Allsway Building, better known as Harker Hall. Reflecting the nature of her catalyst, Ilsa is scattered and not completely "all there."
Ilsa was almost killed by the Malchai Sloan, in This Savage Song. Sloan claims that he killed Ilsa when he is trying to kill August as well.
Ilsa died by sacrificing herself in order to consume the Chaos Eater. She selflessly did this in order to stop it from wreaking even more havoc after it started to materialize into its fully solid form. Quick as air, she went dark and threw her arms around it, causing the room to explode in silver and shadow as a result of the two forces colliding. After the blast subsided, Ilsa reverted back to her human form and began to crack. The fissures spread from her hands to her arms, shoulders, and face before she broke apart shattered onto the floor. The last August sees of her is the look of utter sadness in her eyes.