"You're the one assuming I'm over confident." She didnt even know why they were fighting. She was helping and she was good at it. Sure, she was young but who could blame her for her age? It was better than running around scared and getting hurt that way. And it wasn't as if she was chasing after deatheaters. She was part of the group that was just trying to stave them off.
But she might have moved, intending to get away from the guy who thought she wasn't good enough to help. He seemed determined to follow her though as she threw a temporary blindness curse on one of the deatheaters that moved close. "Quit focusing on me and help people!"