I wouldn't say Naya is evil, as you do get to know her better and see the pressure she has as an incompetent guardian. That said, she is definitely not innocent nor sweet: she hunts people for fun, and outside her kingdom's borders (not to mention she doesn't mind chewing on innocent people). Even though she has been warned many times, she continues to do so. and in my opinion that is why a third party has begun to instigate stuff with the war between the two kingdoms, it's because she already has history of making the relationships between the kingdoms tense.
In addition, in the past update, she can eat you, and although you decide whether she eats you or not, the fact that there is a choice shows that she still sees people, even people who she is closer with, as food. If you think that premeditated killing and eating innocent people, while also ignoring any duties to her kingdom is her being innocent or sweet, then we have different definitions of those two words