Some JWs believe that when couples have had premarital improprieties and there are any subsequent problems in the marriage, God's spirit and blessing were never on the marriage because the premarital sins were never "handled." It may be that when your wife spoke with her sister the premarital issues came up as something that needed to be resolved in an effort to save your spirituality and the marriage. As others have said, this is a misguided attempt to straighten things that have nothing to do with your current feelings about the organization. They're so programmed to look inward for blame that she may feel guilty that her part in the premarital activities (and then failing to immediately confess to it) make her at least partly responsible for your attitude about the organization.
Your wife will have to come to terms with this in her own way and time. I hope things go well for you. I admire your strength.