First, US laws don't apply to someone in another country. Second, she isn't a "Debt Collection Agency" since she is the one to whom you owe the money, so the debt collection laws don't apply. Third, what do you mean that she will "continue to harass [you] for the rest" even after you, "pay her what [you] owe her"? If you paid her off, how is it that she is owed even more?
Frankly, there probably isn't much you can do - you could try to get a restraining order, but it cannot be enforced on the other side of the planet - the cops Down Under aren't going to enforce it.
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