Once Rob left Mary at Castiel's request to tend to Johnny, Jo moved over to comfort her daughter. A hush seemed to fall over the room in the moment between when Dean disarmed the woman and made the kill shot. Jo didn't wince, didn't look away. The anger coming off him was palpable, but she had a healthy dose of that anger herself. It wasn't just Dean's daughter who was bleeding and in a bad way. Jo silently inspected Mary's wounds, taking stock and weighing their options. If they were back home, she would have said that they should go to the hospital and to hell with the consequences. But they weren't on Earth. There was no telling what internal differences there might be with the aliens and whether or not bringing Mary and Johnny in would mean that they ended up locked up in some government observation room somewhere. That wasn't going to happen as far as Jo was concerned.
She cradled Mary in her arms and let her daughter hang on as tightly as she needed. There was only the slightest bit of disappointment that they couldn't have inflicted a slower, more fitting revenge. But that was overridden by the relief that it appeared to be over.
She frowned in the direction of Cas, Rob, and Johnny's prone body. She couldn't see well enough from her vantage point, but he didn't appear to be breathing. The gaping hole in his chest didn't look good. She just hoped that he hadn't paid with his life to get Mary back.