Female Golden Retriever Aggression

Question
Ihave a female Golden Retriever who we adopted at about a year and half old. We have had her over a year now. She is wonderful and could not have asked for a better dog. We also have a 12 year old female border collie mix. They have gotten along since day one. In fact bringing the Golden into our family helped with our older dogs weight -she began to play more and lost a lot. With in the last two weeks the Golden has became aggressive towards our older dog with no provoking of any kind. She will leap on top of her and just attack. She out weighs my older dog probably by a good thirty pounds and when I have pulled her off of her back she has returned to her happy loving self. My older dog is in shambles trembling and I have to take her somewhere and calm her. The golden has never broken skin but I am sure that she has hurt her. I have a gut feeling that she is jealous but am not sure why after all this time she is and why it is at completely different times. Once last week she jumped onto her with my five year old between them. One of the dogs bit him during this time. I've went over everything I can think of to figure out what is going on. It's not during feeding or anything that seems to be happening to trigger. Sometimes inside, sometimes outside, morning, afternoon. I just do not get it and am not sure how to fix it. It's not fair to my older dog and certainly not acceptable around my kids. Any ideas what is going on with her and how do I help?

Answer
The key to most behavior problems is approaching things using the dog's natural instincts.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/