Am I understanding that you are all going to make soups which are gluten-free? But she might not like what you cook up? And she's already warned you she is a fussy eater? So she's giving you hints to go practice soups to see if you think she will like them? I'm sorry but this sounds beyond -way beyond - discourteous to me.
A can of tomato soup is gluten-free. Chicken broth is gluten-free. Vegetables are gluten-free but grains are not. A cube of beef boullion or a can of consume is gluten-free. There's an easy answer.
Good luck Sasserfrassers!