Symbolism, Imagery, Allegory
Did you notice that everyone listened when Diido sang "The Lament of the Pearl Diver"? And by everyone, we don't just mean the fish that are supposed to listen to her since she's a koi-boi. Check out what happens:
As she sang, she saw the yellow roiling river of the City, the City that had been home. People came to the doorways of their huts and tents and sat, drawn by her voice. (8.21)
Diido's voice has near-magical properties. Maybe she could moonlight as Ariel… Anyway, Diido's song is a symbolic shout-out to the Sirens of Greek mythology. These ladies had powerful voices, just like Diido—and just like Diido, nobody could turn away from their songs.
Need a refresher on these alluring mythical ladies? The sirens lure sailors to their deaths by singing to them. In their defense, though, they're trapped on an island with little to do besides luring sailors to their deaths—so while they'd prefer not to sing boring songs, since those sailors keep coming, what else can they do? (At least this is Margaret Atwood's take on things.)
Just like the Sirens, Diido is trapped in her world. Her songs might seem magical and wonderful from the outside, but Diido is faced with a horrible ultimatum: Get raped by Tseri, or be kicked out on the streets (and probably die). Tough choice—in fact, some might say it isn't a choice at all.