Okay I did watch the video about Sea Fairy's character and I understand her better, but I still don't like her. I just dislike her less.
But while watching this video, I've always wondered, it must be hell to be a god you know? It must be boring and annoying to hanndle all the responsibility for centuries or even eons. I mean, especially if you were born to be just that. We know that Fire Spirit, Frost Queen, Stormbringer and Nether Queen were ordinary cookies before turning into the elementals.
Sea Fairy just appeared and given a role and big duties. It doesn't surprise me that she isn't really emotionally healthy. She is closed off and doesn't have anyone to talk to about her problems, except the other elementals. But I think she just doesn't even think about telling them. She still cares about her people and the living beings in the sea but Kingdom didn't exactly give her a good spotlight.