It's a human emotion, but it's a terrible human emotion.
She used her precious tool as bait, she went to murder mode without asking, and most importantly, she lost against some unarmed guy with no training even before he had any power. If the main character hadn't been paralysed by shadow monsters, he'd have gotten away entirely. And almost immediately after that, her life's been saved by the main character.
She has a fraction of shadow talent that got to her head that she can't even use efficiently to capture the main character, she's a liability that gets oneshot and she's angry that someone else got the stuff she wanted. It's understandable, but also being a total bitch - with her position as "head" she also has a duty not to be a petulant child. It'd be nice if one of the elders had pointed that out, that she'd failed that badly as a head and tell her that her abuse of someone who's shown to better her thrice (shadow powers, saving her life, evading her murder attempt) should have her stripped of her position.