I think you have nothing to reproach yourself over Amy, your conscience should be clear. Many other drivers who don't drive to the conditions would have killed him.
Without wishing to trivialise the matter, I would beat up on myself if I had run into an animal, because it feels pain and neither me nor you would want to cause pain or suffering.
But we live in a big enough blame culture without foisting it upon ourselves when we are not at fault!I agree you should distance yourself from the mother. She may read into it that you have no compunction but that's
her problem to be frank; she should look in the mirror and ask if she has anything to reproach
herself with instead of putting you on a guilt trip.
Biological problems aside,
anyone can have child but it takes something special to be a mother or father! In the animal kingdom, the parents pass their wisdom onto the offspring instead of just blaming the State or anyone else except themselves!
By the time my daughter was four or five she was showing
me how to cross a road properly, I taught her!!! Before that her hand was super-glued to mine or she was under supervision. Where is that today???
Oh!!!, but they will drive the kids to school every day and back because the world is replete with pedophiles and perverts!

You sound like a lovely, kind and caring person who wouldn't harm a fly Amy. Live your life and don't give it free rent in your head anymore; life is too short and for what it's worth coming from a complete stranger reading your post you didn't do anything wrong...
Kind regards and

Tony