There are some leaps in your post that would be in medal contention.
Based on the OP it COULD be an emotional issue, but just as easily a physiological or even a psychological issue.
People use all kinds of terms to describe those they have sex with; BF/GF, partners, playmates etc. Everyone has their preferences and possibly terms that annoy them, even terms swinging & lifestyle raise some peoples ire, but to each his own. As long as it is not disrespectful then what is the harm. Particularly with the term Mrs., which I occasionally use as well. Heck her screen name is even MrsCoupleErotic and she is the one that decided to use it.
I think the bigger issue in the OP is what caused such drastic change in her sexual life. What, if anything, can or should be done about it. It is unusual for someone to go from swinging to celibacy in such a quick turn without some underlying cause. But Grabby has been around the block a few times as has his wife, so I wouldn't think jealousy or betrayal or self esteem would be my first guess as to what is going on in this case.
Grabbyzz, have you tried talking to her about it? What does she say?