Fins are forever - Tera Lynn Childs

Just when things seem to be going swimmingly, Lily Sanderson's human-hating cousin Dosinia is exiled from the mer kingdom of Thalassinia and sent to land, leaving Lily with the huge task of keeping her on the straight and narrow.
But why was Dosinia exiled in the first place? And why, why, why is she batting her eyelashes at Brody, Lily's former crush?
As if her bratty cousin weren't enough to handle, the reappearance of a merboy from Lily's past makes her question her decision to renounce her kingdom and stay on land with her boyfriend, Quince.