I thought we all stopped wasting water like this decades ago!
Is yours one of those apartment blocks where the OC pays one water bill for everyone? If so, perhaps start a conversation about moving to individual metering. When our OC did that many years ago, we had the advantage that meters were already in place. Having data that highlighted that a very few residents were using grossly more than everyone else helped to pursuade owners to move to individual billing.
Is there someone upstairs of this woman? Perhaps they can be persuaded to provide a deluge on a regular basis!
If you are not a committee member, could the committee make the request in writing through the managing agent? I expect the letter could refer to imposing an unreasonable cost on the owners corporation through excessive water use. The letter could also refer to bylaws about not interfering with reasonable use and enjoyment of another’s unit. Having one’s balcony flooded would seem to fit the bill.