Coffeegal - I think you should definitely acknowledge the due date. Your friend will already be thinking about it and upset, so you acknowledging it is not going to all of a sudden remind her “Oh yah, I was doing great, but now I have to think about that again”.
Pregnancy losses (esp later ones like your friend had) are tough on so many levels, but one of them is definitely that in a way it’s easy for the person to feel like they are the only ones who remember their babies and that everyone else has forgotten and assumes that they are okay and have moved on. Any acknowledgement that this is not the case will go a long way.
That said, I think you have to be a little careful how you do it. I was all over the card idea, but the other posters didn’t like it, so I’ll go with the email suggestion. Sending a nice email saying your thinking of her a few days before the dd is very sweet. I would stay away from doing it in person though.
First off, if she’s in rough shape it could be more stress on her to have to hold it together for you (though of course this depends on your relationship, maybe a good cry together would be therapeutic?). But more importantly, I think there could be some awkwardness since you are pregnant now. So that could be difficult to manage for her, even if you don’t say anything about your pregnancy.
Hope that helps.