The mother isn't necessarily a bad mother. Its not unheard of the let your hands off a stroller for a second to hitch your pants up, scratch an itch etc., and its also not difficult to be standing somewhere and not know that its on a decline. You could see in the video that after one second, maybe one and a half, she went after the stroller and slipped. I saw this on the news, and was actually flabbergasted. That doesn't happen often.
this video does not show it..but the news clips does show her earlier trying to steady it on the incline and it rolling down..she stops it from rolling. Then does it again. We all have those moments some are just at worse times than others.