She need not show more for him to know her injuries are far more extensive. His expression hardens, though it is not directed at her.

"I will not stand for such; you need not fear."

Sansa isn't one of his people, but she is a child who has been abused. Thranduil is not hard-hearted enough to refuse her aid.

"The gods did not bring me to you." however he does take a moment to glance at the trees, "I know the sounds of the forest and I could sense your unease before you spoke." he smiles faintly as a butterfly lands on his shoulder, "A child should never feel fear. I do not know your parents' reasoning for marrying you so young, but I will sunder the bond myself."