***I must apologize for my rudimentary Elvish names; I figured I should give at least some of them names and all I had to go by is my trusty Silmarillion appendix.
The Warrior Awakens
Mirilendilme did not leave right then; for it was not necessary to go straight away. Having assumed the role of ambassador she first went on an errand to visit both Dale and Erebor, taking the initiative to pledge the allegiance of Thranduil to the good peoples of Middle-Earth. She returned and stayed in Mirkwood a while longer to counsel the Captain of the guard in the establishment of fences of security guards around the kingdom. This plan proved helpful, for with the outposts furthest from the Halls of Thranduil they were able to keep updated on the neighboring movements of Orcs and other enemies, and more readily receive news of the outside world.
The King also took her counsel to begin the building of a large supply of weapons and the preparation of an army. In the precious few peaceful moments she now had, Mirilendilme pondered the peaceful bliss of her girlhood, which she had relished for a long age, and which was now fading swiftly into her distant memory. The stern sense of duty that called to her Noldorin spirit somehow brought her comfort, as though she had been waiting all her life for the moment of the Orc attack after the Prince's departure. The Prince! She wondered how he fared in the halls of Elrond, and wished she could be there with him.
Autumn began to wane, and the preludes to winter came gusting in from the North. Then in early December the news came. The Prince would not be returning. He was to be sent South with a small company on a hopeless yet fateful errand, evidently carrying the only hope left for the victory of Middle-Earth over the Dark Lord. Mirilendilme wept, wondering if this was the doom she foresaw. She thought of her father, and the rings he had helped to forge, and of his rebellion against Sauron and repentance to Galadriel and the Elves, when he learned of the One. The One Ring! Surely this was the topic at hand in the House of Elrond. But of these things Mirilendilme spoke only to her mother, who herself had only learned of them from Galadriel after Celebrimbor's death. Now Mirilendilme truly wished she had gone with Legolas; King's permission or no. She would've gone in his stead, to Imladris and most certainly on this journey to the South. That was not a job to be laid so unjustly upon a Sindarin Prince, she thought; responsibilty belonged to her father (at least in part), and vengeance belonged to her. This was her sign. The time had come at last to leave.
Going South
Now, to Mirilendilme's surprise there were many Elves of Mirkwood of a like mind willing to go with her; more than she had expected. She did not need a very large party, so in a speech to them she emphasized the need for their valor at home, where their duty truly lay. Thus she was able to trim the number of down to ten, though still twice more than the party of five she had planned on. Perhaps it was just as well, she thought, that there was a larger party to distract enemy attention from Legolas' company, set to journey the other side of the mountains.
Her mounted company set out west through Mirkwood; reaching the edge of the forest in a week. From there they headed south toward the Old Ford. For a while, even riding through the open fields and thin woods, they found no danger, and even met a couple of the Beornings. She was comforted greatly to learn they kept safe passage over the Road and the High Pass.
They rode southward, with the jagged peaks of the Misty Mountains against their western horizon. In the still moments of dawn Mirilendilme took joy in the rising sun that would light the snow-capped tops ablaze in the dimness of early morning like the stars lit the night sky. The frosts of early December in the Vale of Anduin lay about them in a dreamlike silence. Mirilendilme found it disturbing at times, as it was so quiet that it seemed that, with the exception of the Beornings, all creatures for miles around that may have dwelled there had long cleared the area or lay under the ground, hiding. Surely this was the result of the Dark Lords emissaries who had spent weeks searching the Vales earlier in the year.
They passed the Carrock, and crossed the Old Ford without difficulty. She led her company as close to the river as possible; knowing that the mountains were the abode of many fell creatures. They soon came to the Gladden River, which Mirilendilme had forgotten, and had not paused to consider. The junction of the Anduin and the Gladden was certainly no place to cross, especially not with horses, and they had no choice but to head up river toward the mountains. It took them a several days to reach a place suitable to cross, having dismounted when the foothills became hard to manage. When the sun set on the third day and they continued walking their horses into the night. Through the days, the Elves had taken to singing to cheer themselves in the disturbing silence of the lonely hills. But Mirilendilme bade them silent that night; worried by the looming and infamous peril of the Misty Mountains. Soon the others felt it too; the presence of fell creatures not far away. They came to a bluff over which the river swiftly passed, maybe forty feet in height; and hoped that its preceding waters would be shallow enough to cross. But it was widely surrounded by vertical faces of rock and steep hillsides, and they had to turn northward and hike the long way in order to reach the top. An hour later they were steadily ascending the hill, alongside a thick wood that rose up the Eastern Slopes. They all had been growing ever more wary; hearing less than they could see. Suddenly, from out of nowhere it seemed, a noise whirred through them. Mirilendilme's head jerked up in a start toward the woods. "Yrch!" cried Sirendil, the Elf of the guard whom she had appointed second in command. An Orc arrow had flown straight across his face; missing his nose by a hair.
"To arms!" she cried. Faster than any mortal could reckon their arrows were strung, as they peered into the darkness for a target. Suddenly a rain of arrows flew toward them; past them and over their heads. Now Orcs could see as well as Elves in the dark, and Mirilendilme guessed they must have been just within range – just far enough to more easily miss their targets so sorely. But each Elf was quick enough to pick out an arrow as it flew toward them and shoot in the direction it came. In this way they seemed to have felled several, for their response was quickly followed by dreadful shrieks, then a series of shouts. "Ride! Ride!" Mirilendilme called, and swiftly they all mounted and made for the river.
The Orcs were on the chase. Several poured down the hill out of the thick wood. The Elves turned from where they sat upon their horses (who were making for the river in a fright), and spent many arrows in a few short moments; slaying many. One of the company was shot in the arm, and another's horse, the horse of Galadhel at the rear, was shot in the leg. The company had finally reached the river when the howls of wolves broke the sky. The sound was piercing. "Ai! The Wargs!" said Sirendil, "Hurry!"
"Iluvatar be merciful!" said Mirilendilme, dismayed to have to wade their horses carefully across the river one by one. However most of the Wargs seemed preoccupied with the Orcs (most of whom scattered at the howls). But several Orcs still remained on their trail, and they came and surrounded Galadhel, who, at the rear of the company, was in the midst of crossing the river. Fortunately Wargs also had a hatred for Orcs (at least on this side of the mountains, where they weren't at the command of the wolfriders) and preyed upon them as they did upon the good peoples they found wandering the mountains. Before his Elf companions could even fire at them, four wolves came up the path behind them and broke into the besiegers, and spared Galadhel from death by Orc. But once they had all been slain the Wargs turned on him. The horse continued to reverse in fear, surrounded. One wolf leapt at him, but straight away five of the company from the other side of the river shot their arrows and slew him as he flew. Even as he was slain two others were backing Galadhel's horse, who was bucking and neighing wildly in his defense, toward the edge. The Elves shot at them also, but with not enough time. "Galadhel, jump!" shouted Mirilendilme, and the Elf sprung from his horse as the wolves sprang their final attack, and the three beasts fell over the bluff to the bottom. The last wolf was slain as Galadhel took a seat behind his nearest companion. The cold shrill cries again grew near. Another pack burst out of the woods from on the other side of the river when the company took off. For a good while the Wargs kept up the chase, snipping at the heels of the last Elf's horse. But ere long they were outrunning the Wargs by far. Like a gale they galloped southward, and did not stop until morning.