Simon is obviously smitten with her when they first meet, but she never treats him as anything more than a "mundane" until after his transformation into vampirism. As a vampire, he gets deeper into their world and they become friends. They spend the night together (non-sexually) when Simon attempts to comfort Isabelle after Max's death which she blamed herself for. Isabelle is shown to be jealous of Maia, who also liked Simon. Isabelle's feelings for Simon deepen later into the series, though she refuses to admit that she may be in love with him. In City of Lost Souls, she eventually admits that she thinks about Simon all the time and "nothing like this has ever happened to [her] before". However, she struggles with her feelings and telling Simon how she feels about him, believing that the guy should make the first move (contradicting with Simon's personality who, as stated by Clary, thinks that if a girl does nothing to indicate any romantic feelings must mean that she doesn't like him).