We're leaving out one possibility. Maybe the woman is just plain dumb. Maybe it didn't occur to her it was dangerous?
Not that this is an excuse, but it's a possibility. I have a friend who was a labor & delivery nurse for a long time at a university hospital (large % of high risk and teenage and low-income pregnancies). She can tell you stories that would curl your hair of people (sometimes well-intentioned people) that are just several IQ points short.
I must say, my mother and my grandmother were downright paranoid, and naturally I'm that way too. "Don't do that, you'll get hurt" "Be careful around that table, it has a sharp corner" They were always thinking of some obscure way that no one else would think of, that someone could get hurt or something could go wrong. My husband, who had a much more normal mother, has had 20 years to get used to this constant apocalyptic "Oh, no! What if...?" He still shakes his head at it. There's a lot of reasonably normal stuff I never got to do as a kid because something might get broken or dirty or I might get hurt. Now, lest you think I believe I missed out because I didn't get closed in a washer, I don't.
This rather rambling tale is to try to make the point that some mothers are hyper aware of what could go wrong, some are normally aware, and some apparently are hardly aware at all. In the animal kingdom, survival of the fittest usually ensures that mothers with bad parenting skills reproduce less than mothers with good parenting skills.