Purpose of the hanky?
doesnt seem to do anything or did I miss something?
shareHelped the girl escape.
shareYes, but the reason Karen put it there in the first place felt forced. It didn't feel like Karen at that point had any reason to suspect that she would be captured. And what good would that hanky do if he grabbed her and locked her up in another room..?
shareAgreed.
She put it in there like she was planning to get locked up, which isn't a good plan. If she felt like Kevin was abducting people, she could have used the bathroom and then left and alerted the authorities, or she might have returned later and tried again herself, better equipped for Kevin.
She literally only got herself killed since the other girls were disemboweled by the Beast, he/it surely would have noticed Casey's scars in the process and let her go anyway.