If her instinctual idea of fire is that, wouldn't she choose another magic "instinctively" too?
Something that she feels could hurt someone without even thinking about it, like lightning for example.
Feels like she's bringing out fire simply because manga logic says fire is first.
I'm not saying she should win her first fight or show off some mega courage, just so you haters are clear on that, just questioning why fire would pop out there.