I am so sorry for the loss you have suffered. It's not going to be easy to get through the grief, but it will happen. Most of all you need to give yourself the time you need, and spend a lot of time doing things you think will honor her and her baby's memory (such as donate time somewhere, volunteer if you can, or just help and talk with her friends and family about what she meant to you.)
I am not a religious person and so I feel there is no consequence passed from one "being" and even if I was, I could not believe, in this case, that the punishment would fit the crime. In your case, your remorse is plenty at this point. Some people suffer more bad luck than others, and to me that is simply all there is.
I do wish you better times and I hope you find some small measure of comfort in the memories you have of her. I wish for that to grow into more of what you think of when you remember her and her baby, rather than the loss. I know from past experience that it does happen, and I am working towards that with our most recent loss of my nephew...it is nowhere near complete, but I feel it in that sometimes when I am remembering something he did or said, or in a place where he was also, I hear his loud, gruff voice and see his smile and hear his laugh rather than think entirely of the fact that he will never be there again, I think just maybe he "is" there if only in my memories and those that loved him (and there were many).
Your friend is not as gone as you think she is, and you will discover that as time wears on.
My best wishes to you,
Liz M.