oh good choice in music!
It's hard to come up with stuff that would fit Thalassa becasue my own taste in music normally means I'll think of something that parents probably wouldn't let their kids listen to becasue most of these songs are full of death... all the good songs about water this kid would probably be obsessed with are all about drowning people or war or something like that.
but to at least pick one song I can see them really enjoying Daughter of the Sea.