For all Galadriel's "magic" (of course, the Elves don't call it magic) and foresight, Celebrían never had much of it, and what she had was much more subtle. Save one occasion that even her mother could not decipher.
As a small elfling Celebrían had never seen an Orc and had hardly been told of them, and yet she had constant nightmares of orcs. No one could explain this.
(Note: I believe that at the incident of the Redhorn Pass with the orcs that Celebrían was raped,, as is implied by Tolkien, and I don't think tiny Celebrían quite had nightmares of that, I think she just had unclear dreams of being in an Orc cave, knowing she was afraid, and seeing Orcs, which would be terrifying enough for an elfling. In this headcanon fic when Galadriel see's Celebrían's dream she sees more detail than Celebrían ever does, due to her own power.)
Eventually her parents convinced her that if she could learn to fight she would be able to defend herself in her dreams and have no more fearful nightmares and, once she had begun to master the sword, it worked.
It was many, many years before the incident at the Redhorn Pass, but when it happened, Celebrían felt many details of her horror was familiar, because she had had nightmares of it as a child.
It wasn't until millennia later that Celeborn and Galadriel realized that they should have taken these nightmares much more seriously than they did, that they should not have forgotten them, and this increased their guilt over what had happened.
Galadriel had not been very deeply asleep, and had awoken instantly when the door to her chambers slid open ever so slightly and Celebrían crept in on light feet. She sat up, which woke Celeborn, and Celebrían's fearful eyes shone out at her through the darkness.
"Another nightmare, sell-nîn?"She said quietly and softly, and Celebrían nodded tearfully and ran to her.
Galadriel lifted her easily onto the bed when her daughter threw herself into her arms and a small sob sounded.
Now Celeborn sat up too. "This is the fourth time this week, Brí." He said worriedly, stroking her hair. And the third night in a row. He added mentally to Galadriel, who shook her head.
"It was the same one." Her high, small voice was muffled against her mother. "I keep seeing orcs…and they're black and hairy and then there's this huge one with mismatched ears and teeth and a horrid face and they're all scary. And they smell of….death"
Both her parents suddenly frowned. Celebrían had never seen an Orc, they were sure of that. How did she know what they looked like?
"Celebrían, dear, has someone shown you a drawing of an Orc? Where have you seen them?" Galadriel surely hoped no one had shown or told her elfling what an Orc looked like, briefly wondering who would be suffering her wrath come morning.
But Celebrían just shook her head. "I only ever saw them in dreams."
Galadriel and Celeborn frowned at each other, but decided where the nightmares came from wasn't the most pressing matter at the moment.
At her daughter's bidding Galadriel sang softly to her until Celebrían was calm enough to be persuaded to try sleeping.
She curled up between them, her arms wound around her mother and her face pressed tight against her. Safe in her parents' arms, she finally drifted into a peaceful sleep.
Darkness. She was somewhere in a cave. There was no light anywhere, and she had no recollection of how long she had been in this cave. Perhaps forever. The fear and hopelessness in this darkness was too thorough for any memories of light to slip through.
Her hair was matted and tangled… she glanced down at it. The gold- no, silver, when had it become silver? – was streaked with blood, and she realized the blood was her own. Her eyes traveled to the weapons and knives littering the cave floor, also coated with her blood.
She was too weak to lift a limb, she realized, and she jumped weakly and frightfully at a noise above her, though her mind was too foggy to even remember why she was afraid.
Then she remembered. Orcs.
The image morphed. Then there was pain, though she knew not where it came from. She heard loud noises and realized they were her own screams…why couldn't she stop screaming?
A gray Orc, monstrous, appeared above her and she realized she was tied down. She tried to escape the ropes that bound her as his knife pierced her arm, but the Orc only tightened the bonds more and struck her, mercilessly laughed at her pain.
Why couldn't she stop screaming…
"Galadriel!" Celeborn's concerned voice cut through her sleep and she awoke suddenly, realizing she was drenched in sweat and that Celeborn and Celebrían were sitting watching her, Celebrían on his lap and pressed frightfully against her father now.
"What…oh…Celebrían, I'm sorry child, everything is all right now…" Her voice shook even to her own ears.
Celebrían was shaking too, and she now moved to hug her mother.
"Did you have a nightmare?"
"Yes."
"You had my nightmare."
Galadriel didn't answer, watching Celeborn instead, and Celebrían pulled back.
"Wait a moment." She said authoritatively, and slid out of the bed, running out of the room.
"Where…?" Galadriel asked, and Celeborn shrugged.
"She is right, I did have her nightmare." Galadriel told him fearfully. "Celeborn, what was that? How could she imagine such things?"
"Later…" He muttered softly, for Celebrían was back.
"Here!" She thrust the sewn cloth horse Galadriel had made for Celebrían at her and climbed up behind it. Galadriel had made it for her when the nightmares first started, hoping a comfort animal might stop the nightmares, and had told Celebrían the horse could join her in her dreams and would carry her away from any danger she might encounter there. It hadn't worked.
"Maybe she'll help you, if she didn't help me." Celebrían told her mother hopefully, and Galadriel broke into a smile in spite of her worry.
"Thank you, my dear." She murmured, pulling Celebrían close and pressing a kiss to the top of her silver hair.
"I can sing to you?" The elfling suggested, and Celeborn told her it was a wonderful idea.
Celebrían sang the one Galadriel liked to sing her best, though she forgot half of the third verse, and Celeborn helped her. After the fourth Celebrían started to grow tired herself, so Galadriel picked up for them, watching Celebrían drift off to sleep again and watching Celeborn follow.
Then she laid her own head down, her arms around Celebrían and Celeborn's arm draped over them both. She closed her eyes and tried to calm her still racing heart.
If it had been a nightmare of her own, she would likely not have been so afraid, but the fact that it was Celebrían's made it so much worse.
But, she thought as she started to drift, opening her eyes again, tomorrow would bring what tomorrow may bring. Tonight, her family was safe.