Daryl had pulled Beth from the prison, telling her they had to go. She followed his lead because she knew she had to, but she left with a fractured, aching heart. She had no idea what had become of her sister Maggie, dear sweet Judith, or any of the other children. She wanted to stay and search, but the prison was overrun with walkers, the fences destroyed by the Governor's men, and Daddy was dead. Running kept the vision of his gruesome death at bay. Maybe that's why they ran until they finally collapsed in exhaustion. Maybe that was Daryl's plan. To keep her moving so she didn't have time to break down into a useless sobbing mess. If she was running he wouldn't have to deal with a distraught girl who just lost half or family. It was like he was trying to keep her so exhausted she'd forget everything that had happened. Or maybe, he was the one who needed to forget.