B: Thanks for your well sourced comments.
I have always thought that Mary really didn't understand the enormity of what was going on. If she truly knew Jesus was God incarnate, how could she raise him as a normal child? How could she rebuke him at the temple and not understand what he meant when he said he was at his father's house? How could she come with his brothers to take him home when he had started his ministry?
I think Mary did understand, at least in part. The Bible says she pondered these things in her heart. Also, she didn't rebuke him after his comment about His Father's business, but before. She knew that He could do something about the wine situation at Cana. But, she wasn't a perfect person. So I think while she understood that her son was the Son of God, she sometimes didn't know how to handle that information properly.
I would tend to agree with that. I think that the idea that Mary was instantly aware of her fulfilling the prophecy in Isaiah is an interesting hypothesis that has no scriptural support: the Luke's chapter does describe her mental state, and it describes it as confusion rather than an "aha moment". Later, she is described not quite understanding her Son as He stays in the Temple. The Church does not call this ideas wrong, but it is but a hypothesis, and it seems at odds at least with the above episodes.