Welcome Brandigirl, first off, you are a good mom for coming on here, and asking for advice. Honestly, i had to smile when i read your story, she wants to belong to you, you belong to her, and she doesnt like the idea of having to share her mommy.
I would let her have "time out" when she's acting like a bratt towards the other one, what you could try is, picking them up at the same time, have them on your lap together, and talk to her, tell her what she's doing is not nice, they DO understand!
Who was there first, your yorkie or your Shih Tzu?
Yorkies do love to be showered with attention, the world belongs to them, and she's not shy to show it.
I'm sure there are more people on here that have dealt with a similar situation that will gladly help you.
Good luck, and keep us posted
