Cute idea! I think the most important thing at this stage will be to make sure it's clear it's a hat, and it's hers, rather than a thing sneaking up behind her trying to devour her head. (Design-wise I really like #3, but it doesn't quite read as her hat.)

Thank you for the tip!
I thought that she could maybe conjure demons or something like that so a monster on her head doesn't really sound like a bad idea to me. But yeah, I thought that it was obvious that it's a hat, but from an outsider's perspective, it isn't really that clear huh.

While we're at it, could I ask for your opinion on the color scheme? I'm not sure whether I should go with a more monochrome style (like #3) or something with more neon colors (sort of like the purple in #2).