This is obviously not about anything we normally post about, but I am really looking for some help,

Over the past couple of weeks our female Flat Coated Retriever (5yo) has been attacking our older (17yo) Great Dane/German Shepard mix. This has never happened before. Whenever there is any excitement, me coming home from work this evening, or last week when she got a bath, she just goes insane and viciously attacks the older dog. It is really bad, like she is trying to kill the older dog. Then when things calm down, she is fine and acts like nothing happened. She even eats next to the older dog twice a day without any incident. We do have a third dog, a 1yo Golden male who is best buddies with the female nnd gets along great with the older male.

I have had dogs all my life of every kind and never seen this type of extreme behavior from pack mates. There always is some jockeying for alpha position, but nothing like this. The aggression is counter to her nature. She is generally a shy girl who one she gets to know you will want to climb in your lap for a cuddle. She is not overly protective of the house. All my dogs are fixed, so there is no breeding tension here.

We are going to take her to a dog behaviorist. But I am afraid that we may need to give her up. Mainly because we are very worried that she may turn on the golden once the older dog is gone. At 17 we don't think he will be around much longer. He has doggie Lupus and his hips are going. Naturally we would rather he goes softly than being torn up. We have taken to separating them (the old guy is locked in a dog pen) during the day when we are at work. Any suggestions on what the heck is going on with her?