Another thing to keep in mind is that the VCAA defined 'expository', 'imaginative', and 'persuasive' aren't clear-cut extremes that we must choose from. Of course for SACs your teacher's words are gospel, but talk to her about it too. You could consider a hybrid, or a blend- really you can write anything as long as it ticks the boxes (as abc said relevant to prompt + text/film, with cool ideas, and engaging writing). From what I've heard from assessors, they really dig entertaining, engaging responses, and it's often those that stand out from the cliche expository discussion of ideas and examples that show these ideas that score the nines and tens. In my opinion, writing creatively (there are more means to write creatively than a short story) comes with an inherent risk, but if it's something you really enjoy, and are good at, it can really pay off, both in personal passion for writing, and in the enjoyment of the assessor. I think there was a really good creative response in one of the examiner's reports (for conflict iirc), I just can't remember which year :/
If you're teacher was similar to mine, I'll assume she's wary of creative pieces because the majority of them are done really really badly, as you effectively have to 'show' the ideas of your context, rather than explicitly expose them. Have you shown her one of your creative responses (if not perhaps do so in a practice sac)?