Welcome to the Bunnings Workshop community Rebecca (@Beksta). It's amazing that you've joined us, and many thanks for your question about hanging mirrors.
What type of hanging mechanism is on the back of it, perhaps string or a hook? How thick is the hardwood ply it is going to be hung on? With these extra details, I trust our helpful community members will have plenty of suggestions on how you can hang your mirror, so it doesn't fall off the wall.
I look forward to hearing further details and assisting in providing a solution.