I neither like or dislike Nia, and I have no problem with people who have valid reasons for their likes and dislikes. But you're coming across as a rabid fan here. Her eyes and hair and "zomg Mary Sue even though the author created her" are not really well put reasons to feel so strongly against a character. If you can't come up with something more articulate, such as "I really can't relate to characters who are naive" or "I prefer female characters who go into battle." I would just keep this yourself. Because most fandoms WILL react badly to rabids.