Walt thought he saw a teenager not from the crash in the forest. But then again he also thought he'd seen his mom. He was probably hallucinating. So why did she seem so alive? And why did she glow whenever he saw her?
Walt was walking in the forest with Vincent. Not all the way in the forest, just enough to still see the beach and be seen by his father. He walked in a circle then found a tree and sat down. He looked up and saw his mother looking at him and smiling, like this was where he was supposed to be. Then his mother disappeared. In her place stood a teenager, not known to be on the plane. She glowed a pink and purple color, like she was some kind of ghost.
He knew he was hallucinating this but he couldn't bring himself to move his eyes from her. It was like she was trying to tell him something. When he heard his father calling him, he stood up, glancing away as he stood. When he glanced back, she was still there, waiting for him to make his return to the beach. He didn't see her until a couple days later. Only this time he wasn't alone. Kate, Claire, & Sun were with him. They were collecting firewood. He suddenly stopped and looked up. The lady's looked at what he was looking at and saw the glowing girl.
She was still visible as they made their way back to camp with the wood. This time Walt decided to say something. Everyone got together for a meeting and Walt brought the mysterious girl up. Kate, Claire & Sun vouched for Walt saying that they'd seen her as well. But Walt told them that this was the second time he'd seen her. And that's when she showed up in front of everyone, claiming that she knew a way off the island.