Both my miscarriages happened after I had my three girls. So I bet she probably feels some of these things:
*She knows what it's like to be a mother and the intense emotions you feel for your child. She was probably already experiencing them for this one.
*She might be being told to just be thankful for what she has and that some people don't even have that. Well, she isn't some people, she is her. And this hurts her. Of course she is thankful for her children. That doesn't mean this baby didn't matter.
*People will tell her it's meant to be. And she will think, "it's meant to be that I hurt?!?!? It's meant to be that MY baby should die while crackheads get pregnant over and over with babies they don't want?!??"
Definitely let her know how much it sucks. That her baby meant something. That it's ok to feel sad!!! Just because it is natural doesn't make it easier. Tell her you are there. I wouldn't say it everyday. But I would make it a point to say it again in a week. And again in another.