If the Mod C question specified for us to use a persona or character from one of our studied texts for Mod C can we write our piece from the author's perspective if there are no characters? E.g. Spotty-Handed Villainesses by Atwood
Perhaps you could assume the author herself is the main character/persona since she is the one giving the speech and since there are no other characters as you mentioned? There doesn't seem to be a viable alternative to this approach as using a persona/character from one of the prescribed Module C texts as a basis for a response is essential in terms of answering such a question.
On a side note, I would assume NESA designs their Module C questions in a way that doesn't cause such limitations/difficulties, meaning they consider all their prescribed texts for the relevant module when designing their questions, which would in turn suggest that the questions (in this case Module C questions) are designed in such a way that allows students to use any of the prescribed Module C texts to write a high-quality response without causing a disadvantage that could result from a potential incompatibility between a Module C question and one (or more) of its appropriate texts.