A friend of mine had luck with the Thundershirt for her girl who was suffering separation anxiety. The only caution I would give is to make sure your apartment isn't too warm so that she doesn't overheat in it. (I'm the kind of person who like the thermostat a little higher than most people)
A doggy friend could help, but is not a guarantee that neither dog will suffer separation anxiety when together.
Another friend takes her dog to doggy daycare because of separation anxiety. I know this is a huge investment and not always possible.
Your Yorkie is very lucky to have a loving home with you and I hope that you can resolve her anxiety.
__________________ Kristin, Max and Teddy  |