It wasn’t her fault.
She’d gotten shots before. Lots of them. They’d never bothered her. Orochimaru-sensei had always been taking her blood and injecting her with stuff too and she hadn’t expected a routine vaccination before a mission—the first one the village was willing to let her take part in since Shimura-sensei had taken her in—to be any different.
She didn’t know what’d happened, exactly, just that she’d seen the needle and kinda completely freaked out. She was pretty sure she remembered kicking somebody, and biting somebody else, and then she’d been running. One of the medics had chased after her but she was fast and lost the guy as soon as she got outside, dodging into the streets and disappearing among the people there just like she’d learned how to do after Mom died.
The panicky feeling was a lot harder to shake, though, and she was completely winded by the time she got to Shimura-sensei’s house. She let herself in, terrified of the medics finding her if she stayed outside long enough for him to come to the door. Turned out he wasn’t even there anyway, but his house still felt like him and it helped her calm down enough to breathe right again. Still, she couldn’t seem to stop shaking; she ended up hiding in his study, huddled under his desk where the light didn’t really reach, focused on regulating her breathing and chakra signature just in case the medics really did come looking.