My neighbor just died from giving child birth , why ?

I am in shock she has two other small children and all was fine , she was happy , excited and couldn’t wait to bring her new baby home, the baby lived .
We live in the US and I haven’t heard of this in over twenty years , they are doing a autopsy though I still don’t understand what could have gone wrong , do you have any idea’s that may help me to understand ?
Thank you for your kindness