Does she know "leave it"?
One of the people whose dog I help train had this issue with a puppy attacking their older dog starting around 8 months of age and practicing "leave it" worked for them. I don't think it was as bad as your situation, but she said she was afraid the puppy would literally kill the other dog. This puppy was also very reactive to people going by the house, unfamiliar sounds, etc.
She practiced this by:
Increasing the dogs exposure to things that arent "hers" to handle and then teaching "leave it".
Taking the dog out on leash and teaching her to "leave" other dogs alone that pass by: turning her around and walking in the opposite direction if she starts barking and lunging, forcing her to sit calmly as other dogs walk by.
Having her pup practice leaving alone other things that aren't hers - your items, guests, etc. and practicing with treats and toys with a release command.
This might not help everyone, but it helped her and we taught Warden "leave it" because he was also reactive to strangers and other dogs when we got him. He's gotten a lot better but I dont think these cases are as bad as yours :-(
Hope I at least helped a little... good luck
Warden - Sable GSD 4/23/2013
Blackjack - Black and tan GSD 4/23/11-6/1/2012
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