Oasis69, as you say, clearly she’s inconsiderate and so are her friends most probably.
I agree with Whale on most points but will suggest something extra, whether you are an owner or tenant; and I guess the balcony-chatter is a tenant as you mention the ‘agent’ which I assume is the real estate agent.
Go to office of the real estate agent, find out who the Property Manager is of the balcony-chatter’s property, speak to that person; follow it up in writing. See if you can find out who the owner of the unit is, write or contact them; again put it in writing. Maybe pay them a visit if you get an address.
You could also pay $40 to inspect the ‘strata roll’ at the Strata Manager’s office, which I think you would have a right to do. Or the Strata Manager might simply tell you how to contact the owner, or even speak to the balcony-chatters on your behalf. Tell the strata manager your problem anyway, they may help.
Basically, you need to be AS annoying to the real estate agent and owner of the balcony-chatters property, AS the noise is annoying to you. And you need a multi pronged approach. (Not much point in engaging with the balcony-chatter herself anymore.)
Be prepared for a bit of stick, especially from the real estate agent. Property Managers are ‘bottom dwellers’ and like an easy life. If they won’t help you, you may have to find out who the boss of the office is (licensee) and annoy them, which won’t endear you to the Property Manager but may get you a result.
You sound like a nice level-headed, even-handed person but I encourage you to go the whole hog and don’t hold back.