Iacisrmma- are you saying that there is a halacha that it is assur for a woman’s elbows or knees to ever be revealed any time she is in shul even if there are no men present? Obviously, people should try to be tznius at all times, but I never heard of a specific halacha like that – which doesn’t mean it doesn’t exist. Does it? Where does it say that? And is that only during davening times?
And if that is the case, why doesn’t every shul have a sign posted saying that it is assur to enter if your knees, elbows, collarbone, or hair are uncovered?