I wonder if dogs can sometimes see angels that people cannot. When an angel appears on earth, it’s not as a cute harmless little winged infant, but as a mighty and fearsome being, glowing with fiery energy. A dog might realize this is something definitely bite proof, and cower, even if the angel intends no actual danger to it. It would have been the angel that came to escort your wife’s soul to eternity.
A very real possibility.