Cheese Extract - How to Use it?
Cheese is often in a recipe for texture as well as flavor: it is stretchy and creamy, as well as "cheesy." One exception would be sauces, or baked into a casserole, in which the cheese is all melted in and is almost entirely there for flavor. I'd suggest attempting a cheddar cheese roux sauce, using soy milk instead of dairy milk and adding a small amount of the cheese extract.

You will need to experiment to get the proportions right, so hopefully your sister likes mac-n-cheese :)