Many pet owners make the mistake of thinking fearful dogs have likely been abused, when in fact it is often the opposite! Dogs that have been given affection without consistent discipline (and exercise) often display insecurity and anxiety.
We humans mistakenly try to comfort them as if they are humans, when in fact what they need is correction and confidence. Encourage a nervous dog by being a calm, strong leader and they will follow. If your dog is anxious and you give her affection she will see this as a reward for her nervous behavior. When your dog is anxious she will likely display displacement behaviors such as shivering, panting and yawning.
Many pets become “unbalanced” when they do not have a consistent leader and this often leads to behavioral issues such as aggression. Often these issues will worsen over time. It is important that your dog knows you are the leader and that you understand the signals your dog is giving you. One good fundamental tip is to make sure your dog never goes through doors ahead of you or pulls on walks. A dog with a pack leader is a happy dog!