Jack rolled her eyes at Elijah's words, knowing better than to take anything he said as seriousness, because he was one of those ego-boosting people that seemed to swarm Hogwarts. She did not mind of course, because she would be the first to admit that her pride was almost as large as the castle itself, and she made no attempts to humble, especially when she felt justified in it. Which was most of the time. As in, basically all of the time.
But at the moment, Elijah's cockiness was not a pleasant distraction from memories of tear-ridden friends and hate-filled rivals. She thought his lightness in the situation was rather aggravating, especially because she had not seen him do anything to help the situation. She did not mind if you were simply unable to do something, but incompetent, lazy, and cocky? No thank you, she did not like the combination in this particular setting.
Her irritation was burst when she began to really process the situation between Elijah and Chase and she felt anger boil inside her. Chase was flirting. So much for distraught, dumped Chase. Jack much rather preferred the lying Chase who had hidden her relationship with Andrew to the one who flirted with sleazy Slytherins and troublesome poltergeists. Jack felt her hands quake with anger and she thrust her hands into her pockets, turning to leave when Chase beat her.
She paused; she had no aspiration to follow Chase, but she would not stand being couped up with Elijah nor his fangirl Brienne. She would take her chances outside. She stepped outside the compartment and her fierce eyes focused on Elijah. In a 'don't-test-me-just-enjoy-yourself-here' tone of choice, she said, "Well, you have fun. I'm going to close the compartment door, and I'd love if you would do something right and stay put." She closed the door and tapped the lock with her wand, as she had done with the other compartments before hurrying down the aisle.
She overtook Chase in no time, and as she pushed past her, she could not keep herself from growling under her breath, "It's okay, Andrew's not around. Who's to tell if you and Elijah get cozy, eh?" The snarl sounded half between a muttered musing to herself and a threat, but there was no doubt Chase heard it. Jack quickened her pace to go find an adult and something to do. She needed to distract herself by taking on some actual adult responsibility, unlike the children she had just abandoned.