I., I have 5 children, but 4 are living. My 3rd child was stillborn (died June 11, 2004 and was born June 12, 2004). We miss her so much! I think I can help answer this question.
As others have mentioned, we all handle grief differently. My husband and I are laid back type of people. We weren't angry, but very, very sad. We talked about Abigail a lot and still do. She is a part of our family. We don't mind people talking about her. We have never cried so much in our entire lives. Even though sometimes talking about her gets us teary eyed sometimes, we love talking about her. The intense pain does go away, but it will definitely take some time. Just for the future, hopefully your friend won't mind you remembering her birthday. We just took flowers to our little girls cemetery plot on Memorial Day. Our kids love to go visit.
Giving her a plant to remember her child by would be great! We cherished our mixture of greenery for a long time and took care of it. If you were/are able to get the blanket and cap that was next to the baby's skin and have it put in a shadow box...that would be awesome too. We have a picture of our daughter in our living room. The doc and nurses took tons of pictures. Hug her and cry with her. Her child is a special child that had a different mission on earth. She came, got her body, and went back Home. She didn't have to be subjected to this life, thankfully, but was given a different calling...a special calling. That in itself gave us, my husband and I, even more meaning in life to do the things that we need to be doing in order to see her again.
There isn't much a person can say that will offend me, but I had found other people that were offended by what others said in similar sad times. So I thought I would put some of those down, just so you'll know to avoid them. Not that you would say any of these, but sometimes, people just don't think or know what to say or what not to say. I would NOT say, 'You can always have another one.' or 'It was best this way.' (especially if something was wrong with the baby). 'It was meant to be.' We just don't want to hear these things at that moment. Even what I said earlier..some aren't ready to hear, but others are.
Just be there for her, let her talk it out as much as she needs to. I have friends that remember our little Abigail's bday and that is so neat! I don't expect anyone to remember her date or put flowers on her grave.
You can get together some friends to provide meals for her each night for the family for about a week. Maybe go over after the busy-ness is over and expect to be cleaning up a bit.
I had some other stuff in the back of my head, but it has left me now...I think I'm tired...got some kiddos to get to bed now. Thanks for listening to me this long.