Again, if the assumption is Mary is planning on having children with Joseph, then upon hearing she would have a child, why would it make sense to immediately ask how that would happen?
I understand your question and have tried to answer it. Again, here's mine, if Mary was planning to remain a virgin, why tell us she was betrothed? The normal thing for the culture is to be fruitful and multiply.
There is no "immediacy" imparted in the angel's message before Mary says this. She has not been "asked" yet in order to give her "consent". She is only told she "will" (future) have a child.
Not to derail this, our tradition includes many things not found in scripture and it supports the explanation of her response traditionally given.
Nonetheless her response does not make sense in the context of a plan to have children with Joseph. To say it makes more sense to disregard the stories we have from tradition because they are not "scriptural" and assume instead that Mary sensed "something", some "immediacy", we do not have in scripture does not work for me. How is that assumption more "scriptural" than our tradition?
It is also a bit odd to say she senses urgency in the message, meaning she will soon be pregnant, and having her say "I do NOT know a man". If she expected from the angel's saying she would have a child to be pregnant that night, wouldn't it make more sense for her to say something about Joseph, the man she alledgedly plans to have children with? Does this version also happen to require Mary to be blonde?
She was betrothed, promised, engaged, but they weren't yet married.
Look at Zecharias and the angel's "same" announcement and "same" reaction---one of disbelief (note the mood tense mentioned earlier).
John announce: But the angel said unto him, Fear not, Zacharias: for thy prayer is heard; and thy wife Elisabeth shall bear thee a son, and thou shalt call his name John.
Jesus announce: And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
John reaction: And Zacharias said unto the angel, Whereby shall I know this? for I am an old man, and my wife well stricken in years.
Mary reaction: Then said Mary unto the angel, How shall this be, seeing I know not a man?
So, the angel makes a promise and the reaction is similar, how? For all we know, Mary may have thought herself barren, like Elizabeth, her relative.