My fear would be what if something happened to her while she was out? What if she got hit by a car crossing the street, and was rushed to the hospital with no one knowing her baby was home alone?
Far-fetched, of course, but not outside the realm of possibility.
I understand the fear, but still, exactly the same thing could happen at home. What if she fell down the stairs and broke her neck? Stabbed to death by a fake courier driver? Freak electrocution accident? None of these things are "outside the realm of possibility" but at some point you need to draw a line about what you worry about.
That's not to say that it's unreasonable to draw the line before "popping 100m down the road for five minutes", but it would also be fair to say that the realistic chance that something is going to go devastatingly wrong is vanishingly small.
I mean, I often read stories in the paper about scenarios where parents have left small kids at home for hours on end while they go drinking at a neighbour's place or at a pub a short drive away. That's obviously negligence pure and simple, but kids actually survive that level of neglect (relatively) unscathed all the time, so there is a very large greyscale between "I would freak out walking to my letterbox while my child naps" and "They'll be right for a couple of hours, we're only next door."
