Strictly speaking metalanguage means language about language. In the context of a text response I don't think this quite makes sense. Here are some examples of what I think your teacher might be looking, not all of which are examples of metalanguage:
Juxtaposition, antithesis, deconstruction, socio-political context, foreshadowing, metaphor, symbol, subversion of the reader's expectation, prolepsis, analepsis, alliteration, irony, metafiction, character foil, romantic irony, past-tense, first-person narrative,
stream-of-consciousness, etc.
These aren't great examples, since I got half of them from briefly reading some of my essays, but it should you a sense of the general flavour of what I presume your teacher means. I sincerely doubt she wants you to analyse how the language is being used, using the term metalanguage was probably just a gaff by her, she probably just wants you to talk about the techniques that are being used by the author.