We have three dogs. They were in the house with us, but if another dog had been anywhere near our yard, they would have sounded the alarm. Besides, I don't think a dog would have taken one hen - without a trace - and left the others alone. Dogs aren't that "dainty" if you know what I mean.
Going to keep holding out hope that she is hiding and will show up tomorrow. I know, it's foolish of me.