You know, I side eye a lot of things, especially asking people to bring a secondary gift, but this isn't one of them. I actually wouldn't have a problem with it. I'm going to assume that as a parishioner, it's costing nothing/ very little to hold the shower there? The way I see it, that favor by the church is passed onto me as the guest, b/c the hostess is able to use her budget more more food/decor/ things to make me enjoy the party more. So can I bring a.79 can of something? Sure.
It's not MTB asking for something for her, and I always welcome the opportunity to take a step back from the "me, me, me" world and realize "I have the ability to buy a friend a nice gift and spend the day with her eating cake. Some people can't and would be psyched to have the can of green beans"