Lapis does have her own theme in the series, which is pretty telling: "I Am Lapis Lazuli"

As far as I'm concerned, this one fits her extremely well: "Shatter Me"

And this one's a little abstract, but . . . I think probably the experience of watching/listening to this one is probably a lot like trying to listen to Lapis's song at times, if that makes any sense: "Goodbye to a World" - lots of spoilers, though! And flickering light, if you're sensitive to that.