Jo wasn't opposed to being the hardass. In fact, she was pretty stubborn and didn't always possess a whole lot of tact. All the same, she was surprised at just how much she was going to have to play that role because Wash clearly had a soft spot for the kid. She gave him a look at the "she wouldn't do that." question.
"Wash, that's exactly what she did to Sam. I'm just lucky that she casually mentioned that the dog she brought home had been a random guy at the bus stop."
Whether he was going to be the softie or not, Jo really wanted to impress the seriousness of this situation on Wash.
"There's more." She frowned, clearly wrestling with herself about how to word the next part. She felt a certain loyalty to Sam and Dean and while she'd told Wash about the life that she herself had led, that didn't mean that she was interested in naming names and calling out other hunts. And yet... he needed to know what could potentially be a concern down the road. That not everyone in the City might be as accepting of her powers if they couldn't help Maxine get them under control.