I also would send her a card and maybe even a tiny little gift. I was given a tiny crystal dummy (mine had a pink ribbon on it but I know you can get somes with little blue ribbons) which I think is just gorgeous (not expensive this one as I brought one later for my friend) and a lovely keep sake which isn't in your face either. I'd stay away personally for the time been with your baby as it could rub salt into her wounds that you have your son earthside and she doesn't. In time she will probably love seeing your son as it will remind her of what her son would be like and what he would be getting up to.

My friends mother lost her son at a few days old and now 25years later she still loves looking at a lady from her churches son (whom was born a few days apart) as she said it reminds her of her son and what he would be like (size, age, milestones etc)