What you are seeing is not jealous. As dogs do not think in that manner that is a human thought and not a dogs.
What you are seeing is dog on dog aggression and a needs to be addressed with a trip to a Behaviorist, or to a trainer that is working in the aggression Field.
Also you have a teenage dog (18 month old) that is well being a teenager but the more she gets to practice the bad habits the more ingrained it will become.
I have a little light reading in th form of aggression book if your interested Pm Me.
I have work now for a while with my girl and her aggression and am off in the New Year to see an leading trainer in aggression and use my girl as a training dog in the seminar.
This is the Field I love to work with and talk about.
joy |