Hey Byron, your original title was “Common Property Dilemma” – hardly stands out from the crowd if you want an instant answer in a thread about Common Property.
There’s not much you can do to force the upstairs owner to accede to your plan unless you have more than 75 percent of the Unit Entitlements (and I’m guessing they’ll be more like 50-50).
Talking is always the best way and in your case you need to bring enough sweeteners to the table to make the upstairs neighbour WANT to do what you want, rather than just allow it.
Find out what would make this an attractive proposition for her then add a bit more. Once you’ve got agreement, it’s just a case of getting it all in writing so everyone can agree and sign off on it.
But make this a positive move, rather than a challenge to her rights, and that will go a long way to you getting what you want.
You could go to Fair Trading with a case about how the upstairs use of common property diminishes your value, with claims about noise and inappropriate behaviour or whatever – if you want to turn your home into a war zone for the next few years.
Talk and, even more important, listen, and you might just get what you want.