Subha’s name means “sweetly speaking.” The literary device that her name ilustrates is IRONY since the girl cannot speak.
The literary device irony is defined as a literary technique, originally used in Greek tragedy, by which the full significance of a character's words or actions is clear to the audience or reader although unknown to the character. Irony involves the employment of a language that normally signifies the opposite, typically for humorous or emphatic effect.
The name is an example of the rhetorical device of irony. Irony refers to a situation in which what is said by the author differs significantly from what the reader expects, or from what is actually the reality. In this example, Subha's name means "sweetly speaking," but this is ironic because the girl cannot speak.