Few things...
One, is it possible that you're wife is trying to "protect" you from possible confrontation with the sister being in the house? I don't know all the details of your situation, but if you are fading, DFed, DAed, whatever...she may be thinking it would be awkward for YOU.
Second, is it possible that you're wife is trying to "protect" herself? Maybe she's nervous about what the brothers and sisters will say about her with having a husband that is fading, DFed, DAed, whatever...she may be fearful of the awkwardness for HERSELF. She may know this sister is going to leave your home, call everyone she knows on her cell phone and say, "I'm housesitting for Sister Jourles and her husband. I just left their place since Sister Jourles was showing me what to do when they're gone. You know what? He was THERE! And he is red and scaly with a bifurcated tail and carries a hayfork."
Third, it might be a good time to pull the "I am head of the household" card even if you are fading, DFed, DAed, whatever. As head of the household, you do NOT appreciate her storming out, do NOT appreciate her not communicating what her true feelings are, do NOT appreciate being asked to leave your own home. I hate to recommend this, but if you feel it necessary, it might help "tone" the situation down a bit. Or pour accelerant on the fire, I don't know.
Just my couple a cents,
Andi