Congratulations on getting your first Yorkie. Based on her weight at 12 weeks, I would think she will be around 3 lbs grown. Do you know what the breeder is feeding her? In the beginning I suggest you feed her what the breeder has been feeding her and hopefully it is a quality food. Personally, because of her size I would recommend the Solid Gold Wee Bits. You can go to
Http://dogfoodanalysis.com and click on reviews to read about the different dog foods available. Personally, I would recommend getting one of the 5 star rated dog foods. I feel that many of the 6 star food are not suitable for yorkies because of the high protein content. Best of luck with you new baby. We will be looking forward to seeing pictures.