My husband's grandmother alluded to the same thing--something like, "God has a plan and there must have been some reason for this." I don't know if she meant a specific physical reason or what, but I bristled at it because it sounded just like the kind of words I remember people saying when I was younger and one of my cousins had a miscarriage, words I accepted at the time but now I completely disagree with: "These things happen for a reason... there must have been something wrong with the baby..."
When we got the autopsy report and there was no identifiable cause of death for my daughter and everything stupid thing on that list was marked "normal," I was devastated but I also felt sort of vindicated. Here I held scientific "proof" my baby was perfect (except for the no-heartbeat part). But now I see that was wrong, too. Because even if there had been something "abnormal," even if there had been a chromosomal problem or a physical deformity or a specific problem with her heart, had my baby lived (and many babies do), no one would have dared say that she was less than perfect. Perfection isn't some kind of universal standard--it's the measure of how much she was loved and wanted and cherished. To suggest that any baby, whatever the circumstances, is not automatically perfect in the eyes of those who love her, it's nothing less than unbelievably rude. To try to dress it up in the guise of condolences is cruel.
I know that our babies were perfect. By anyone's standards.
Besides that, your baby girl was wanted and loved just the way she was. And that automatically makes her perfect.
I'm not sure I would have been quick enough to say something in that moment, either--reflexes are slow when you've just been flattened by grief! But if it would make you feel better to send an e-mail or letter later on, don't hesitate to tell this friend how her words made you feel and how wrong she is about the claims she made. I agree with Mandy S.--she's looking for a way to make the world make sense. But random, terrible things happen to perfect babies and to good mothers all the time. It doesn't make any sense at all. We just do the best we can to create our own meaning out of what we end up with.
I am so sorry about the loss of your perfect daughter. My heart goes out to you. You're not alone in this--in feeling the grief or being insulted by well-meaning people. Hang in there.