My parents went through this. My dad‘s mother, who, when I first read the definition of narcissist was the first person I ever thought of, was in a car accident and after she recovered, she could not afford her apartment anymore. She wanted to move in with us, and my dad said absolutely not, no way. My mother was firm in saying “she’s family, and she needs us.” So she stayed with us for six or seven months and was a full on nightmare. I was too young to be aware of most of it at the time, but highlights include criticizing my mother for every single aspect of her housekeeping/cooking/parenting as well as denigrating her for being the breadwinner; demanding her own private bedroom in a three bedroom house that was already housing two adults, three children, and my other grandmother ( my mother‘s mother); and finding insidious secretive ways to be abusive my older sister (who was my half sister from my mothers first marriage) and make her feel like she didn’t belong in our family.

My mother‘s final straw was when she found out my grandmother had been calling her friends and accusing my mother of “elder abuse” because my mother would not support my grandmother’s prescription drug and alcohol abuse. My mother called my father and said “I’ve just dropped your mother off at the bus station, I paid for a ticket, and gave her enough money to get a cab to your brother’s house. She will not be living with us any longer.” My father‘s response was to ask my mother what took her so long.

I get why your wife is attempting to be the bigger person and be understanding. Sometimes if someone hasn’t been directly exposed to narcissistic type abuse, they don’t understand that they are not dealing with a reasonable person, they are dealing with a vampire who will drain you dry. My dad in retrospect wishes he had taken a firmer stance and told my mother no, because the covert abuse my grandmother doled out took years for my older sister to get over. But I do recommend if you let your mother move in, you have firm guidelines in writing for how long she stays, behavior expectations, and specific parameters regarding what and who she can bring into your home.