Rose couldn't take much more of this arguing. Neither of them were handling it particularly well, but Rose knew what it was like to not have a father around growing up, and for a same-but-different version of him to show up later.
"Oi!" she yelled. "Shut up, both of you." She had her arms crossed over her chest, glaring at them both. "Jenny," she said, turning to the girl. "The Doctor helps people. He isn't asking you to just stand there and watch people get killed. He just wants you to try to find alternative ways to help. Which we know must be hard for you, since you probably never learned how to do that." Given that she was only six months old. Here she turned to the Doctor, making sure he was paying attention, and would cut the girl a little slack.
"That's why we're going with you," she told Jenny, determining all this as she was going along. "You can shoot the zombies and skeletons and such, and we'll find ways to handle the things that can be reasoned with. Right?" It was a question, but one the Doctor probably wouldn't want to answer 'No' to.