I'd personaly stay away from Science Diet and Royal Canin, they both use too much fillers.
Here's a great source that will give you an idea of the best dog foods available
www.dogfoodanalysis.com/
If you're going to switch foods, check out this list first, it'll give you a better idea of what's best for your Yorkie. Yorkies are notoriously picky eaters (including mine
) so some canned food mixed in with the kibble helps, the chicken like you are doing is good too (just make sure there are no spices or oils used for cooking). Alot of people on here also sprinkle parmasan cheese on their dog's food to entice them to eat (dosen't work for mine though). I personaly use Orijen puppy dry and Evenger's canned mixed together, both great foods, but there are many.
Adding vegetables and a little oatmeal to her food like you said you are is great too