Hi,
I have been through he same thing with my dogs....
I have a training tip that has worked with 4 dogs so far
Put your dog in the submissive position ( on her back with your hand on her throat) and put the chicken directly over her. Keep the chicken over her and release the neck but make sure the dog stays in that position until you decide to take the chicken away and tell the dog to get up. This works best with 2 people ( 1 with the chicken and 1 with the dog).
We know dogs have a pack mentality and in a family situation with weaker animals in the pack the dogs need to be at the bottom of the chain.
This will work for also for rabbits, ducks,etc. My sister in law told me of this technique, after she trained her Wire Haired Pointing Griffin (HARD CORE BIRD HUNTING DOG ) this way and now her chickens freerange with that dog laying beside them and goes hunting on the weekends with my brother for grouse
It also worked for me with a new dog we got and it only took a couple times of putting the chicken over her and now she doesn't even look at them.
Sorry for your loss... it is frustrating and sad...
Try this method... it is a great feeling when you can let the dog out without having to worry about what they are
getting in to