"I'm allergic to trouble. It makes my hands itch." What does this declaration say about Shayla's character?

This shows that Shayla doesn't like the feeling of doing something wrong, and she rather do the good thing to do.

Explanation:

Being "allergic to trouble" here is obviously an exaggeration, but it does its job. From this sentence, we can infer that Shayla doesn't enjoy breaking the rules or getting into trouble. This most likely means she's a well-aligned student/person who doesn't like stirring up problems.

— Hope this helps ♥