He orders her to be confined to her chambers for three days.
This will allow her a chance to become accustomed to her new circumstances, so that she can familiarize herself with moving about in a space she knows before being released to move about the halls at large. Thranduil sends someone to check on her each day.
The first day he is told that she is lying in her bed, crying, and refusing food. He feels a twinge of concern, but brushes it off. It is the first day without her sight, it is understandable that she will be upset and frightened. It will take some getting used to.
The second day finds her up and about for a short while, navigating her room, groping for walls and furniture as she shuffles about. She is still quite upset, still refusing food, but seems to be doing better. The informant tells him that she is making note of everything's location, that she might find it more easily in the days to come.
The third day she seems to be in about normal spirits, and has apparently managed to bathe and dress herself, braid her hair, and buckle on her knives, even if she has mismatched the colors of her clothing and a half dozen fiery red strands escape the usually pristine braids. She does not speak to the inquirer he sends, but she accepts the bread and fruit that they bring. He allows himself to relax a bit at the news.
Thranduil sends a guard to follow her around on the fourth day, should she choose to leave her room. He does not give a reason, though some in his kingdom assume it is because he would not have a traitor wandering unguarded. Thranduil is willing to let them believe what they want, as long as he knows that there will be someone nearby should Tauriel get lost or get into trouble without her sight to aid her. However, she does not wind up leaving her room, and he extends his order for the next week.
It is almost two weeks before Tauriel leaves her room, and when she does so it is in the middle of the night. After the fact, a part of him is annoyed, because sneaking out in the middle of the night is just like her, but on the other hand, she can no longer see the rising or setting of the sun, so he cannot truly bring himself to blame her for the timing.
The soft sound of footsteps and brushing cloth catches his attention as he is running a comb through his hair, preparing to retire for the night. The moon is high in the night sky, and he wonders who would be coming to see him in his private chambers at this hour. The door is open, and he watches it as the footsteps get closer. He makes no move to stand, but is confused for a moment when a hand comes into view, groping for a second in the open doorway, before it is drawn back and the fingers lightly follow the frame around. Tauriel appears a second later, walking slowly, her hands tracing the wall, and Thranduil feels his eyebrows raise to almost his hairline. She does not seem to take any notice of him, making her way slowly but confidently around the edge of his antichamber, and he rises silently to cross the room. He stops about a foot behind her, following her at a slow pace, curious as to what exactly she thinks she is doing. As she nears the pool of water in his chambers with no signs of slowing her pace, however, he makes his presence known by clearing his throat sharply.
Tauriel must have thought herself alone, for at the sudden noise from right behind her she whirls around to face him, milky eyes wide, and stumbles a few paces away. They both realize her mistake a half second too late, and her foot goes over the edge. She yelps in fear as she falls, and he leaps forward, making a grab for her arm, but he misses and she lands in the pool with a splash. She thrashes about for a second in a panic before he has a chance to drop to his knees, grab a hold of her upper arm, and haul her up onto the stone floor beside him. She is coughing and gasping for breath, and he takes the liberty of gathering her soaked hair and wringing it into the pond as she gets her bearings.
"Are you all right?" he asks her softly once she's caught her breath, and the color drains from her face. If she was surprised before, she is frightened now, and she tries to scramble back from him, but he has a firm hold on her arm and keeps her in place.
"M-my Lord! I'm so sorry! I- I must have taken a wrong turn..." she ducks her head sharply, and Thranduil has to lean back a bit as she nearly collides with him. He is not used to this more clumsy, more mousy Tauriel, and it is a long second before he can reply.
"It is all right, child," he says at last, reaching to unfasten his cloak as she trembles and drips before him, "you are not harmed?"
Tauriel shakes her head as he drapes the cape about her shoulders, tugging it to cover her.
"Where is it that you were going at this hour?"
She flinches, curling in on herself even more.
"I...I was trying to find my way to Legolas' room..." she whispers, her head hanging. "I used to go there all the time as a child and I thought that I remembered the way clearly... I must have missed the hallway..."
He stares down at her as she fidgets, looking at the ground to avoid his gaze even though she can no longer see it. Gently he takes her hands, draws her to her feet.
"Come. Let us get you back to your room."
She looks torn for a second between protesting his help and obeying his command, but he doesn't give her a chance to decide, wrapping an arm about her wet shoulders and guiding her carefully toward the door. She falls into step with him, her muscles tensing slightly whenever he changes direction or pace. They do not talk with one another on the way back, and he only speaks when needed.
"Stairs. Fourteen of them. Careful." "Watch your step, the floor is uneven here." "There is a slope ahead, go slowly." "Do not be afraid, I have you. I will not let you fall."
Her jaw is set firmly, and he does not look at her face as she tries to work through mixed pride and emotions. It takes them only a few minutes longer than usual to reach her room, and she gropes in her pocket for the key, both hands running along the length of it to turn it the right way before reaching a hand to search the door. He reaches out after a second, taking her wrist and gently guiding her fingers to the lock. Her movements from here are fluid, and he has no doubt that she has spent time practicing. Once she is safely in her room, he bids her good night and gets a whispered "good evening, My Lord, thank you for your help" before she closes the door. He hesitates for a second, but then turns in a whirl of silver robes and makes his way back up to his chambers.
He will send someone to fetch his cape in the morning.