The second is probably what you want. The now in the sentence refers to the present moment, but it describes a situation that exists now, that she is not in Australia any more. It doesn't tell you exactly when she left.
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AnonymousIs now a specified time?Do you mean like "5 o'clock in the afternoon"? No, of course not.
AnonymousHow do I say it?You probably want "She has now left Australia", but you can put "now" at the beginning or at the end as well.