Assuming that she knew that she had been immaculately conceived (an interesting question in itself), wouldn't it be logical for her to wonder why?
Certainly. But to assume that she would deduce the right answer herself is not shown. In fact it is contra-indicated by, among other things, her questioning the angel at the Annunciation. If she had had it all figured out in advance, when the angel came to tell her she would conceive miraculously, her only response to the angel appearing would be along the lines of "You're finally here!"
How we are to deduce from Joseph's reaction that he was aware or unaware of Mary's perpetual virginity is lost on me. Can you make anythign of it?
SD