You don't just kill a dog because it is killing your animals. That is SO unfair. The dog does not know any better, its a dog. The chickens should stay in there run if the OP wants them to live! If its to small, make it bigger. The owner of the dog probably loves it! How horrible that would be to kill a beloved pet!! Thats why.
First off, it wasn't even chickens, it was guinea fowl. Secondly, the OP can do whatever she wants with her birds on her property. She could give them all little unicycles and teach them to juggle chainsaws if she wanted. Point is, those birds are protected on her property. They don't have to stay locked in a run 24/7 for fear of marauding dogs wandering by and deciding it would be fun to murder them.
If she was negligent (like the dog owner in this situation is) and her guineas were in the street out in front of her property or miles down the road and they got killed by a dog, cat, motorist or otherwise, it's obviously her fault for not keeping them on her property where they are safe/protected, just the way it's the dog owner's fault for letting the dog run wild off of their property where it's not protected.
And like bobbi-j said, once that dog trespasses on someone elses property and starts killing their beloved pets/food/source of income it's a predator that needs to be taken care of. If those dogs had just wandered onto her property peacefully and not done mortal harm to her pets I'm sure she wouldn't even consider killing the dogs, but they're not sweet little pets, they're killers.
If you'd really just stand by and let a dog murder your birds because it "doesn't know any better" then I don't think you should have birds. Our birds are completely dependent on us for their well-being and protection, and if you're not willing to kill an animal that's actively ripping them apart you have no business keeping birds. They're relying on you and you're letting them down in the biggest possible way.
Would you not kill a raccoon or a fox either because they're just trying to feed themselves and they don't know any better? (I honestly feel worse for the wild animals because they don't have anyone to protect them from the natural consequences of their instincts). If the owners of those dogs love them so much, maybe they should keep a closer eye on them/not let them off their property where anything could happen to them.