IMO the entire thread is based on nothingness.
Why does the Op presume that there * has* to be a clash between SB and Tznius? As many others have said, it is not too hard to gently disapprove to ones wife.
If the Op feels that telling off ones wife for a breach of halacha inevitably becomes a SB issue, I wish him much luck if he discovers his wife texting on Shabbos or eating treif.