Sadly, I do think it is sometimes an adoption thing. A while before we adopted ds, while I was still having fertility treatment, three of my friends had babies. Despite it being quite hard to join in (emotionally) Idid join in with the baby shower. This was from a circle of NCT friends (we have a birth DD then aged about 7, now aged 11 so all these friends had similar aged children to me and the babies were their number two, three and four respectively for them!).
Anyway when I was able to announce a couple of years later the happy news we were adopting. At the time a good friend said she would organise a baby shower (same group of friends).
It never happened. She just never did it despite being one of my closest friends.
But luckily my work organised a joint shower for me and another woman who was adopting.
And I still have a gift token to use from that shower!
I never had a baby shower with DD (it was not so much of a 'thing' then) and I think in your shoes I would tell your closet friends that you would like a shower for your little one. Whether this is before they arrive or not.
You and they will need to adapt things as baby showers can be quite 'baby' centred (our DS was three when we adopted him) and also things like bump painting are out (although I have a big bump tummy and am regularly asked when my baby is due!).
It might be that people are worried about getting things wrong and so upsetting you - so make it clear if it would be more upsetting for this special event not to be acknowledged.
Also, it is best not to assume a case of 'I did this for you, so you do it for me'! Better to say to friends or family something like - "I would like a baby/New child shower but (if you agree) I can help organise it" So you could find someone else to help if this friend is not very forth coming.
This may be a good time to make wider family part of your plans or even reconnect with wider family as well as friends, if appropriate. Do you have any sibling/mum/mum-in-Law/cousins/friends who might be better able to organise it than your new mum friend?
Really, it should not cost a lot if all those coming bring a dish, a game and a bottle! And it would be a baby shower where the mum-to-be can drink! Good luck.