Legolas had found the woman trapped by his father while on a scouting mission. He'd been a bit cofused about why a tower was in Mirkwood, and even more so when a woman leaned out the window and shot an arrow at him. Luckily, she had been aiming at the spider coming towards him instead.
They spoke after that, but Legolas left quickly, thinking it as a hallucination.
Life continued for him after that, When he saw her again, he had nearly forgotten about her. She was still firing arrows at spiders. Legolas asked her to help him up to see her. If this was real then he would be able to get up inside.
She threw him down a rope and he climbed up.
Inside, there was a collection of archery equipment, books, a couple rooms, and food. He'd touch various things to see if they were real.
"Is something wrong?" she asked.
"No," he said. "No..."
He began to visit her. She seemed excited when she did so. During his trips he began to notice more and more things about her. She had very long hair, even for an elf. Her archery equipment was top of the line and her food some of the best, but she never seemed to be allowed to leave. Worst of all, though, was that she spoke of Thranduil. Was his father forcing a woman to stay there? He'd heard of it happening, but it was by cruel men, not his own father.
Finally, he confronted her about it. If his father did such a horrific thing then... Well, he didn't know, but he would have to do something.
She started to laugh. "It's my job to keep this area of the forest free of spiders," she said. "It's easier to not get killed doing it up here."