I noticed this too and thought the same thing. I personally would prefer she found a hobby or spent time with her grandchildren than sitting in the corner staring at everyone who walks through line. She is supposedly keeping an eye on the cashiers as per an employee who mentioned this.
Her name is Susan and she is usually jist sitting there waiting for a friendly conversation. She is not abke to run around and stock shelves so she gets to relax and people watch. She is very sweet and is always willing to talk, i am sure she is not scowling but just trying to see you clearly as her vision is not the best.
She's most likely just tired, and taking a break.
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