Do you live in the country? Is it possible your dog is hearing wolves, coyotes or coyo/dogs? I've noticed the time you mention is when packs in my area become vocal, although it never seems to bother my dogs. It's possible your dog is reacting to something only she hears, and I find wild canid packs are most vocal in late fall/winter/early spring. I often hear them around 3pm on cold, clear nights when leaving for work, it doesn't have to be a full moon.What DOES bother my guys is the presence of bears, fisher cats etc around the property. If you have lynx or cougar in your area, they really seem to stir things up.