It would be best to ask a strata lawyer for advice. On this forum, everyone volunteers an answer and we try to be helpful. We are not lawyers. Your problem seems like an expensive one.
You need to determine what is common property and what is not common property. Every strata plan has a document called the registered plan. Your strata manager should have a copy of the registered plan. Otherwise, you can get it from the NSW government. By convention, thick black lines represent common property. Internal walls are usually not common property. My understanding is that waterproofing is common property.
Your problem is that the damage has extended to other parts of the villa. The definition of common property is not that the there is a common wall between the bathroom and the next room. It is usually the roof, floor, external walls, external windows, external doors, slab between floors, walls between lots. As I said, it is shown by thick black lines on the registered plan. Also, common property is not carpet, paint or wall paper. Those things are stuck onto common property but they are part of the lot.