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
I think the line of reasoning was that, if he knew that she had taken a vow of perpetual virginity, then any pregnancy must be virginal and via divine action. So he wouldn't have been upset or surprised or wanting to put her away.