The Flying Mermaid. Volcano Chronicles, #1.5

Craw city has always been magical, at least to Luce. No boring war could ever make her love her seaside home any less. There's the beach, where she and Adu can mess around and cause trouble, as well as the ancient songs they love to sing. Legends state that a vengeful mermaid named Sea Mother will protect the children from war. Why worry about politics and fighting? Nobody would risk the wrath of an angry sea serpent.
Would they? So why are groups of people fleeing the city, and why do Luce's parents disappear every day to partake in mystery war work? What exactly are they doing, and why doesn't Luce's artist mother invite her along? One day, Luce spies something that rocks her beliefs and changes everything. Her faith in the sea, and all she holds dear, will be sorely tested. But love is fierce, and so are sea goddesses. This YA novella can be read as part of The Volcano Chronicles or as a stand-alone.