Mirkwood's Princess - a story about Isilmë, Legolas's sister
I want all to know that I am borrowing Tolkien's characters and making up a few of my own. I take no credit, Tolkien was the Genuis behind it!
Ránalas was her name, she was of the Silvan race. Thranduil took her as his wife, and for many years they lived in the beauty and light of Greenwood. Their children, however, would not know the greenness, for before they were born, the beauty of Greenwood succumbed to the Necromancer, and became dark and full of monsters, giant spiders that were descendants of Ungoliant. But in the realm of Thranduil these monsters dared not stray. The monsters feared the elves, and kept away from them. The elves did not associate with them if at all possible, they knew all the safe paths in the forest and did not stray willingly into the lairs of dark creatures.
When Ránalas bore a son, they called him Legolas, his name meaning greenleaf, in memory of the beauty of Greenwood. The forest was no longer green, and had been renamed Mirkwood because of it's darkness. But Legolas grew strong and was taught in the way of the elves. He became deadly with a bow, and struck like an adder with his knife.
By and by, Ránalas bore another child, a girl. They named her Isilmë, for the light in her eyes shone like moonlight. She had dark hair, like her brother, and if One went somewhere, the other went also. They were inseperable, and Legolas taught his sister to use a bow, and only he was more skilled than she with the knife.