Oh my god, ADA codes, shall I bow at the waist?If they place one foot in or partially in the box. Maybe they put their weight on the foot that is partially in the box and the foot slips. Maybe she has small feet and she stands completely in the box and catches her heel as she backs out. It isn't hard to imagine, which is why you never see shower drains that way.
You can't seriously tell me that you've never slipped or seen someone slip on a small ledge that they weren't expecting.
Maybe you haven't ever had to design or build something, but I have and I have studied ADA codes. That drain in a shower wouldn't pass inspection.