I have heard from a few people in this situation that it annoys them when people don't mention what happened - they feel as if they have to just get on with things and people act like the baby that died wasn't a real person. The worst I've heard is that it's very common for women who miscarry to be told "you can always have another" - you wouldn't say to someone whose spouse has died that you can always have another, would you?
She will be feeling the same as anyone who has lost someone very close to them - grief, anger, disappointment, and she will probably want it acknowledged that she lost someone very important, so I think the best thing to do would be to try and take her to one side at some point (difficult to know when as you don't want to upset her when she has to work) say that you heard about the baby and you're really sorry for her loss. Something as simple as that can be really effective, there's no need to go overboard as you really can't relate to how she's feeling, and I'm sure she will appreciate the simple thought and gesture. You might feel the need to offer support but I don't know if that's appropriate, a simple acknowledgement will probably do. I've also heard that people in this situation feel it's important that others realise that they don't get over these things right away, so maybe you could ask her again in a few weeks time (if you'll actually see her then) how she's doing - this lets her know that you're genuinely concerned and you realise that the healing process takes some time.
It's obvious that you care, so all you need to do is show her this, I'm sure she'll be touched.