'Isabelle will cut out his heart and walk all over it in high-heeled boots.' Isabelle is the best Shadowhunter of her age, second only to Jace. As Alec and Max's sister, she is very intimidating. Isabelle is sixteen at the beginning of the City of Bones. Despite the fact that she lives with a bunch of boys, Isabelle is probably the toughest of them all...even in heels.Isabelle is described by many people in the series as having very striking looks and being very beautiful. She has long black hair that comes to her waist, and black eyes, though she sometimes wishes she had her brother's blue ones. She is almost as tall as Simon and very slim. She wears jewelry frequently, including her ruby necklace sensor, which throbs like a heartbeat when a demon is near. Isabelle also carries a silvery-gold whip she uses to fight demons, and she keeps it wound around her wrist like a bunch of bracelets. Because she is a Shadowhunter, Isabelle is also covered with runes.Isabelle loves to dress out for everything, even while demon hunting. She is described as managing to look like a fireworks display, no matter what she is wearing. She is a very bold and outgoing person, seeming to not be afraid of anything, and trusting few people: her mom, Maryse; her brothers, Alec and Max; and Jace. Despite her hard heart, she is very protective of her brothers. 'But I watch my brothers give their hearts away and I think, Don't you know better? Hearts are breakable. And I think even when you heal, you're never what you were before.' Isabelle has trouble with commitment in relationships. She dates boys she knows don't really care about her, so she doesn't have to be serious with them and make a commitment. 'You know what it never even crossed my mind I wanted? A guy who could make me laugh.' Simon interests Isabelle. She knows that he's average, and she loves that about him. Since she has met him, she is beginning to question how she feels about relationships and making commitments and dating exclusively. She is doubtful of his feelings for her, but he doesn't realize she loves him.