Fred had been looking for Sam for a while, or seemed like a long time. She had to believe that he was okay, and she told herself somehow she'd know if he was gone. Dean hadn't found her yet, so Sam was probably around and okay. Fred avoided the logic in that one, or the bad logic - Dean could be in trouble or as gone as Sam. She just held on to the thought that they were both okay, and she wasn't finding them because they were both busy helping people like they do.
She gave a soft happy hop and sound of surprise when she saw Dean, but her bright smile died as the older Winchester brother walked by her with little thought. She thought she saw tears. She took a breath and started walking faster.
The garage wasn't far away, so she hoped maybe it was something there, something that wasn't Sam related. Dean would have stopped and talked if it were Sam related, wouldn't he? She kept moving, wishing she could run as fast as Flash or something. Maybe Superman.