If the smitten fiancé can't see past this unnecessary and divisive event, to recognize the opportunity to dodge a major future bullet, then he deserves the misery and alimony to come.
Ditch her. Welcome the dog, who has been a joyous part of Christmas in that household for years, and is a loyal and loved family member.
Dogs just have a way of bringing out the basic truth of new people on the scene. I know I trust the instincts of mine, instincts that are in some instances truer than my own. If they dislike a stranger, I've learned to be wary myself.
I had to win the heart of my girlfriend’s dog first. I was OK with it.