I am so sorry that you are having a hard time after losing Casey. It does not matter if she was a mixed breed or a Yorkie it is very sad when a piece of your life is gone. When my kids were very little we had a Lab named Abby and for the longest time I swore that I could still hear her and feel her around me. But I loved that feeling it made me happy to know she was still hanging around. It has been many years since she was with me but I still think about her all the time. It took a long time before I decided to add a new dog~Pebbles my first Yorkie because of how sad it made to to lose Abby. We just lost my foster pup this past weekend and it was very sad to see him go as well.

But I have taken comfort in knowing that he had a very good life while he was with me.
Time will help to heal the hurt and you will always be able to hold on to your memories of her in your heart.