to 'treat' the mum to be on her 'special day' 
Is it a thing now? To ask guests to pay towards the food and decorations??
It's not a surprise shower (mum to be has been talking about it for weeks). The friend hosting has asked everyone to pay £10 towards lunch, cake and decorations. Oh and reminded us all ... via whatsapp group ... to bring a present or contribute to a group present.
IME a baby shower is a sort of party (games, chat) with refreshments and cake provided by the family or host. And gifts of course but you don't mention gifts do you?? It just feels like it's all about the gifts and donating to the 'special day'.
AIBU and old fashioned?