"Hail, O favored one, the Lord is with you!"
  But she was greatly troubled at the saying, and considered in her mind what sort of greeting this might be.
 And the angel said to her,
"Do not be afraid, Mary, for you have found favor with God.  Luke 1:28-30

In the sixth month of her cousin Elizabeth's pregnancy, Gabriel, the angel of God comes to Mary.
Like the shepherds who hear of Jesus birth, she is frightened.
No doubt.
Just think about it. Here is a teen age girl like any teen age girl going about her business. She was not a school girl, but would have been helping out with the household chores. Perhaps she was sweeping or doing laundry for her mother.
Maybe she was alone so the angel could talk with her privately. Perhaps on her way home from some errand, alone in her thoughts when the angel appears to her.

How would he appear? As an angel in glowing tunic, or like they did with Abraham and Sarah, as ordinary travelers?
However he appeared, what he said clearly frightened Mary. He says, "Greetings, you who are highly favored. The Lord is with you."
So you are a young girl going about your business and an angelic being appears and greets you this way. Luke records that Mary is greatly troubled and wonders what kind of greeting this is.
I would think so.

But the angel calms her fears. He says "Don't be afraid. You have found favor with God."
Then he tells her about the child she will have and about Elizabeth's child.

In a moment, her life is turned upside down.
As you know, Mary is a favorite subject of religious artists, and if fact was the dominant theme right up to the renaissance.
In Byzantine art, Mary is often depicted as a mature adult woman around 30 something. Jesus looks like a miniature thirty year old perched on Mary's knee.
But we know she was just a girl and not a sophisticated girl.

Frederick Buechner's little book of character sketches of people from the Bible has this to say about the angel Gabriel as he encounters Mary: "She struck him as hardly old enough to have a child at all, let alone this child. But he had been entrusted with a message to give her, and he gave it. He told her what the child was to be named, who he was to be, and something about the mystery that was to come upon her. 'You mustn't be afraid, Mary,' he said. As he said it, he only hoped she wouldn't notice that beneath the great golden wings, he himself was trembling with fear to think that the whole future of Creation hung on the answer of this girl."¹