“Isabelle," she said, lightening her tone with an obvious effort, "your loyalty to your friend is understandable --"
"He's not my friend." Isabelle looked over at Jace, who was staring at her in a sort of daze. "He's my brother.”

“I should have warned her about your habit of never doing what you're told." Jace squinted at her. "Are those Isabelle's clothes? They look ridiculous on you."

"I could point out that you burned my clothes." -Jace and Clary pg. 63”

“Jace told me once you’d walk all over my heart in high-heeled boots, and it hasn’t stopped me.
Isabelle gave a little gasp of startled laughter. “He said that? And you stuck around?”
He leaned in toward her … “I would consider it an honor.”

“Watching Jace hug Isabelle, she tried to school her features into a happy and loving expression.
"Are you all right?" Simon asked, with some concern. "Your eyes are crossing.”

“What's this?" he demanded, looking from Clary to his companions, as if they might know what she was doing there.
"It's a girl," Jace said, recovering his composure. "Surely you've seen girls before, Alec. Your sister Isabelle is one.”

“Isabelle tugged her tank top back down and glared at her brother. “You don’t knock now?”

“It’s my bedroom!” Alec spluttered.”

“Well, I hate to tell you this," she said, "but your friend is an asshole."
"He's not my friend," said Simon. "And I couldn't agree with you more, actually."
-Maia & Simon about Jace, pg.49-”

“They also said she was unconscious and that Valentine wasn’t happy about it. He seems to be waiting for her to wake up.”
“I’d stay unconscious if I were her,” Isabelle muttered.”

“Simon bristled. She wasn’t his Isabelle, not anymore. He wondered if she ever truly had been. Isabelle didn’t seem like the type of girl to belong to someone. It was one of the things he liked best about her.”

“One of Renee's friends asked her, "Does your boyfriend wear glasses?" She said, "No, he wears a Walkman.”