Had my whole flock of 10 slaughtered by a stray dog. Got rid of it and got babies to replace them. They were big enough to go out finally. Be danged if new neighbors moved in up the road and their dogs wiped out all but 1 of them.
All My Chicks are Missing!!!! - Page 3
Even if your dog did it, there are other predators out there that still might and can. I don't know where you live, but stray dogs, cats, raccoons, skunks, hawks, owls, eagles, coyotes... you name it, they can and will kill chickens.
So first, you need a better pen for them to keep them safe. If it can keep your dog out, it'll sure keep out a lot of other things as well. An electric fence isn't a bad idea, either.
You can try a shock collar on your dog (we needed to use it on one of my mutts. My other dogs are guard dogs, so their instinct is to protect them, not eat them.) I needed to use a collar with a long remote, so I could correct my dog when he couldn't see me, because he learned to stop chasing chickens while I was home, but when I left, he'd do it again. So I had to hide inside the house or behid a tree to do it. It stopped him.
But training your own dog won't stop other predators. You can have dogs and chickens, but your chickens need protection, because they can't always protect themselves, or get to safety quickly enough.
I had originally planned on free ranging my chickens. But after my dogs behavior and hearing all the horror stories here on BYC I decided not to. I am a HUGE fan of chicken tractors and grazing tractors...best of both worlds. Chickens are safe but still get be a chicken and enjoy their small but significant chicken life
So sorry for your loss! I have lost guineas, geese, ducks and chickens to neighbor dogs, coyotes, coons and owls!
Obviously, I haven't given up since I have more birds but I do know how discouraged you feel and how you want to just throw your hands up and walk away. I agree about taking a break for awhile. I know folks out there like yourself that are broken-hearted because now you have a love/hate relationship with your dog who went from best loved pet to chicken killer.
Just take a breather and consider investing in a better enclosure. And if you see your dog carrying around anymore chickens, regardless of how they died, put your dog in its place really quick, while she knows what she's done. Get in her face and give her a good solid 30 seconds of pure heck (nicer word but you know what I mean) and maybe she will get the point. My dogs respond to yelling, so I've got it pretty easy.
But if you are sure it is your dog then she will need some sort of discipline and how you do it to get your point across is up to you. You have to consider now that if she is indeed catching/killing chickens, that makes other chickens in the neighborhood a target too, and someone might not hesitate to take care of the situation with the help of a fast bullet.
Sorry for your loss and good luck. All of the hard work of brooding chicks and them having them gone *poof* is so heart-breaking and maddening. Order a few colored catalogs from some of the well-known hatcheries and take your time browsing through them. Maybe it is time to consider getting some of those 'designer chickens' you might have been eyeing for some time!