Isabelle told her not to tell anyone or he would get kicked out.She was present at Magnus's party, and when they tried to save Simon from the vampires, and when they broke out to war.Clary went with Isabelle and Alec to save Jace after the Silent City was attacked and they found that all of the Silent Brothers had been killed.Izzy also went to the Faerie Court along with Clary, Jace, and Simon.Hearing from her mother that Jace had witnessed the death of his own father, Isabelle, who liked the feeling of being wanted, had expected Jace to come to her like a scared child needing comfort.Instead, she was disappointed when Jace turned out to be independent, brave and seemingly self-possessed, among other traits that slightly reminded Isabelle of herself.
Isabelle lent her clothes and did her hair for her, while Clary finally told Isabelle that she knew Alec is a homosexual.
Early in 2007, Isabelle, Alec and Jace were staking out demons at the Pandemonium Club, a club often frequented by demons looking for victims.
Isabelle acted as bait, seducing and luring an Eidolon demon—who was initially oblivious to the fact that she was a Shadowhunter as her runes were covered with the long sleeves of her white gown—into following her to a supply room, while her brothers followed to kill the demon.
She seemed eager to give everyone the soup she had just cooked and Simon volunteered to try and left Jace amused.
On their way to the library, Jace told Simon that Isabelle would break his heart as soon as she got sick of him.