I don't think I'd use liquid and give it separately because the amount she receives should be proportioned to the food she eats. It would be more difficult if you gave it separately.
You could talk to a nutritionist about using something else (maybe human vitamins cut to her size...they might be less flavored).
Especially with the Balance IT, I really can't blame her for not eating it. It is what Ellie is on and it smells disgusting.
I wonder what bothers her with the Healthy Powder.
Have you tried baking the food with the supplement to see if she likes it? She probably won't but it might be worth a try.