Since she said something that i think was "I will see my home again"
My first guess is that she is from the same city as fizz and go some place then returned later like fizz to see everything gone. She then hears that there was a survivor then join the league. ( Although this may not be true but the despair in her voice imply that her home was lost through violent actions)
Or she is a mermaid living with others of her kind when she is pulled away by a summoner.
Or Nautilus met her in his journey home and sort of kind of "took" her with him :P
Leave your ideas below