We can all make daisy chains of blame, and take on the whole weight of the world. Please don't do that. It's possible that she had a stroke, or that she had a birth defect like a hear murmur; it's not your fault. You didn't neglect her or mistreat her. So it's okay.
Grief is really hard to get through. There is another side, and you'll make it there one day.
When you do, you'll be ready to try again. We have faith in you.