Hello, welcome to YT! Your new yorkie is lovely! I'm glad she is living with you now.
With regards to the food issue - would you consider changing her to a better quality food? Some foods that you might want to consider are Barking Heads, Lily's Kitchen or Land of Holistic Pets. Many members at YT feed Royal Canin Yorkie and Orijen, both of these are available here in Ireland. Nature's Menu do wet food if you want to mix wet through the dry food. A good quality food will help her overall health, including her joints. How much she should get each day depends on her weight and level of activity.
Barking Heads food and Nature's Menu can be bought at Petworld, Land of Holistic Pets can be ordered at dogfooddirect.ie and Lily's Kitchen, Orijen and Royal Canin can be ordered at zooplus.ie. I understand you might not want to feed any of these foods, just giving some options
Looking forward to seeing more pics of your cutie pie