The Roman Catholic Church teaches the Immaculate Conception that asserts Mary was conceived without sin and remained sinless for her entire life. 

Assuming this to be true, did Mary know that she was, in fact, sinless, while everyone else was not? It seems that this would have been obvious. If so, it seems should would probably have expected that God had already selected her for a special purpose. However, she sounds surprised at the angel greets her as a "favored one":

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> Now in the sixth month the angel Gabriel was sent from God to a city in Galilee called Nazareth, 27 to a virgin engaged to a man whose name was Joseph, of the descendants of David; and the virgin’s name was Mary. 28 And coming in, he said to her, “Greetings, **favored one**! The Lord is with you.” 29 But **she was very perplexed at this statement, and kept pondering what kind of salutation this was.** Luke 1:26-29 NASB
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So, again, my question is, according to Roman Catholic doctrine, **did Mary always know that she was sinless**? Or did she come to know that later at some point? If she knew she was sinless, did she realize earlier that she had been set aside for a special purpose?