"Reliquia" by Rosalía uses definite articles and possessive adjectives

Hola Kaitlin C.

Good observation. In Spanish, body parts are often used with the definite article when it's already clear who they belong to (me duelen las manos, se lavó los ojos). However, possessive adjectives are also possible when the speaker wants to emphasize possession or for stylistic effect.

In these lyrics, Rosalía alternates between mis manos, mis ojos and la sonrisa as an artistic choice. Using la sonrisa instead of mi sonrisa doesn't change the meaning, because it's already understood that she's referring to her own smile.

So the song isn't breaking the grammar rule, it's making use of two natural ways of expressing possession in Spanish.

Saludos

Silvia