I have a Yorkie poo (female) and ever since we started walking she was barking at other people. She plays well with other dogs and doesnt bother owners, but she really hates other people. When we have guests over all she wants to do is bark at them like a guard dog trying to protect her territory. If we keep her in a room she yelps and barks until she gives up and whines and whimpers all the time. She doesn't bother us. Any help?

sorry for spelling mistakes I'm on my phone.