The very, very lost girl

13 year old Belle kinderwood lost her twin sister at the age of 6, and missed her very much. All she could remember is her sister loved the ocean, so she went there every day. She knew she was not supposed to go swimming with no supervision but one day she did. She was pulled in by a massive turquoise wave. She woke up on an island that was empty no human life. She had sudden strange cravings and urges and eventually she also had a tail!