While the first part is possible, I don't see how the second conclusion makes logical sense. When she says she knows not a man, why can the leap be made to a person sworn to lifelong celibacy? Any chaste young woman would say the exact same thing.
I will not tire to explain the obvious, no matter how much you prtend not to understand. A chaste young woman betrothed to be married and hearing the prophecy of how great her son will be does not respond "I know not man". She responds something like "I can't wait till Joseph hears this!"