She probably wouldn't have missed that yell, even if it had come through the closed door and not a smashed window. She has both, and she's not actively lacking in a sense of self-preservation or logic. There's a long line of voices in her head. To keep the knife, and that it might not help at all. Even that she could turn away. But if she was going to do that, she would have done it before her hand was on the door.

It's not like his voice told her anything extra that screaming and flying furniture hadn't.
(She would not, she knew quite well enough, too, even be as heavy as the bookcase.)

Still she turns the doorknob, pushes the door open, and maybe she meant to take a step over the threshold of the house, but that was before she could see the house. Everything was everywhere. In tattered, shattered, shreds. It was like a force of nature -- or a monster, her head whispered in, ever helpfully -- had blown through all of it leaving almost nothing untouched. It made the window and the bookcase look light. Even more, Kol wasn't anywhere to be seen.

Her blood pounded in her ears, but she didn't step forward and she didn't look away. "Well, you certainly made a mess."
It's hardly anywhere near the volume she'd used to announce herself, as she was torn between why and how.