One could argue, if one felt so inclined, that the killer driver was as much a victim of the current road system as the child she killed.
I'll bet she hadn't driven very far, so why did she feel the need to drive at all?
Perhaps she doesn't feel safe on busy, crowded pavements.
Perhaps dealing with fast-moving traffic on foot is stressful.
Perhaps she can't walk as far as she used to, but never thought of any other way of travelling.
Who knows?
It could be none of the above, of course. I'm just speculating.