Since we don't have much context, she could be anyone. She might be an ordinary girl with a passion for the sea, or a character created to represent the relationship between humans and the ocean.
The book 'Woman of the Sea' is fiction. It typically has elements such as invented plots, fictional characters, and possibly elements of fantasy or imagination that distinguish it from non-fiction works based on real events or facts.
It's hard to say for sure. Different manga creators have different styles and themes. Some might avoid such content altogether, while others might use it for artistic or narrative purposes. You'd have to look at the specific manga in question to know for sure.