Here is a solution. Use the Cream Soup Mix recipe from Irresistibly Gluten Free (page 14) and leave out the instant dry milk. Then when you are ready to make soup use:
2 tablespoons Cream Soup Mix
1 cup milk substitute (like rice milk or soy milk)
and follow the cooking directions in the recipe.
You can use this milk-free version to make the recipes in the book, just remember, don’t add sour cream to the soup or cheese to the recipe you are making.
I had previously recommended Knorr brand chicken bouillon powder for this recipe, but it now lists barley on its ingredients label. I now use Western Family Chicken Bouillon Granules.