She is not trying to defend you. This is more about her feeling that you are hers and she does not want anyone else taking her place.
As YTjilly said training is the best way to show her who is in charge here. Even simple commands like sit, stay, down, come will help her to recognize her place in the order of things in your home.
Don't forget that training should always be about fun. She should not feel like she is being punished. Don't start training when there is an issue, always do it under stress free conditions and don't forget the treats!
