It wasn't that she was trying to be disrespectful to his majesty or whatever, but he was being such a loser right now and she had no concept of personal space or boundaries. So when he started to boss her her around, she put her hands on her hips and cocked an eyebrow at him. The fire ball trick didn't do anything to deter her attitude, but fueled it instead. "Seriously, you talk like you're in a black and white movie and you expect a little fire to scare me? Think again, Legolas. And, like, no one tells me what to do, okay? So get that straight, elf boy or else I'm not going to answer any of your dumb questions."
And because she wanted to prove how much she wasn't afraid of him, she reached out and prodded him in the chest a few times to make her point. "You." Poke. "Are." Poke. "In." Poke. "Kansas." Shove.
Yeah, so maybe she had some issues, but no one talked to Jennifer Check like she was a five year old. Even if she wasn't all that smart, she had enough pride to host a parade all by herself and she would have appreciated some respect from some guy who looked like he stepped out of a video game.