Hmm well my yorkie girl that I had several years ago was also what I thought was "protective". Ive learned sense then that her behavior was showing she was the "leader of the pack". What I would try is having treats ready in a little bag in your pocket. Start with Kitty outside of the bedroom. When the dog comes to you without aggression give her a treat and praise like crazy. Then slowly work your way into the bedroom. Put a baby gate on the door. Sit back on the floor and keep moving towards the bed and up onto the bed. When the dog is aggressive, without talking pick her up and put her on the other side of the gate. After a little bit let her back in and try a few more times. This may take several days. She should eventually associate kitty with treats and good things.
The potty problem in the house......just be consistant and try hard not to scold to much as the dog will associate potty with being in trouble.
Im sure you will get some other good advice
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