Colloidal silver might not address the root cause, but sometimes taking care of the symptom while making healthy changes is the way to go. I know of a very great many people who have used colloidal silver for dogs, cats and other animals. I have never heard of a single problem from doing so, but there have been a tremendous numbers of positive reports.
An herbal tea might well have very good results, but I would opine that a cat's natural diet would be mostly raw meats and perhaps some fruits and vegetables from forage (cats. like dogs are opportunistic mostly carnivorous eaters) and their normal diets do not include the items that make up many herbal formulas, so in a sense a herbal tea, tincture or other formula is also something that is unnatural to a cat's normal diet which is used to remedy a problem. I would also opine that colloidal silver, which contains nano-sized particles of the valuable and natural trace element silver which mankind has been ingesting in plants and water since we put down our first footsteps in the sands of time, is every bit as natural as herbal formulas which have been processed from natural herbs because one does not go out into the field and find tinctures. teas or other formulas hanging off bushes or trees in the wild.
Don't get me wrong, I have the greatest respect for herbal tinctures (and Uny makes some wonderful ones) and use several, but I also have the greatest respect for colloidal silver and use it both personally and for our pets with wonderful success.
Be very careful with the garlic. Garlic and onions can indeed be harmful and even fatal to cats if consumed in sufficient quantity.