I had a stillbirth at 29 weeks. It's awful.
I really appreciated the texts and messages I got, although I wasn't able to respond to them at the time.
I personally didn't enjoy all the flowers. I remember sitting in the kitchen looking at them thinking 'all this life, all these colours … and it will all be dead in a couple of weeks/days' and just couldn't cope with it. I gave the flowers away to next door.
Plants ditto to a certain extent. We got 2 rose bushes, which we planted. My FIL felt he wanted to do something to help, but didn't know what, he came round one day with loads of plants and did our garden (we're not very good at gardening, our garden looks horrible!), although I didn't enjoy receiving all the flowers I did enjoy looking out on to the nicely done garden. So if you can, do something for them, everyone always mention bringing round a meal, but no one ever did it for us!
Also, give them space to talk about it, don't shy away from the conversation. She's still given birth, she's still held her baby, she's still had her baby, she's still a mum. With live babies everyone always talks about their births, with a stillbirth all of a sudden no one talks. No one asked how my birth was, what she looked like. Some people definitely avoided me simply because they didn't want to be confronted with the fact that these things happen to people like you and me.
Then again, it's so personal how people experience this type of grief. You know your friend best.