Answer:
c. Her mind
Step-by-step explanation:
Byron describes her mind as beautiful and captivating, which reflects through her external beauty that hampers the "nameless grace". He further goes on to portray her external beauty as the expression of her psychic tranquility and purity and puts it in contrary to "blatant" sunlight. He depicts that her facial beauty is the reflection of her pious thoughts and her inner calm, symbolizing the relevance of the beauty of heart and peaceful mind.