Jo hadn't known who the dog was. She'd just assumed that he was some random guy-maybe even one of the City's natives. She definitely wasn't expecting Sam. Her jaw all but fell open in shock when the younger Winchester appeared where the dog had been. There was also a surge of fear as she realized that Maxine's powers might fall within the realm of things that hunters would want to take care of. And if Sam told Dean... well, she wouldn't hesitate to make sure that she protected Maxine from both brothers, but she didn't want to have to be on the defensive against either of them. She moved to place a protective hand on Maxine's shoulder. Sam was talking to her and his expression at least didn't look like the expression of someone who was considering a potential hunt. All the same, Jo knew that she would need to talk to him before he left here.
"Good job," she said quietly to Maxine. "You did the right thing."
She was proud that it hadn't taken much arguing once she'd laid it all out there for the kid. Maxine was still at the age where it was hard to put yourself in others' shoes, but she also didn't mean harm to anyone. She knew just as much as Sam did that Maxine's powers would be dangerous if she didn't learn to control them and if she didn't learn to empathize with others-if she didn't get the chance to learn why she shouldn't use her abilities against someone who was teasing her or some random guy on the street just because she could. She knew that she and Wash had their work cut out for them, but she also knew that there was an innate innocence in the girl that deserved to be fought for and preserved as long as they could. Which definitely meant protecting her from anyone who might want to make a prejudgment on her abilities and whether or not they were safe.