wow, she is growing into a beautiful young lady
i have also heard that it is best to introduce a new one to them when they are younger...that they adjust easier. i have not had any experience with multiple yorkies...we have a 6 year old cocker and 10 year old min pin and they both adjusted just fine to having a puppy in the house...but i have heard more about yorkies not adjusting as well when they are older.
sorry, i'm not much help
but your baby is beautiful!!