Would she then have a better chance at an Australian visa? No, it wouldn't affect it. But why on earth would she be rejected for the PMV? Unless your relationship is not genuine or she (or dependents) would fail the health requirement or you submit fraudulent information, there's not really any reason it'd be denied, and a NZ partner visa likely requires MORE evidence than an Aussie PMV.
Original Nationality: US
Visa #1: PMV (300) through Washington, D.C
Applied: April 2013.
Visa Granted: January 2014.
Visa #2: Subclass 820 (From PMV).
Applied: End of April 2014.
Visa Granted: Early July 2014.
Visa #3: 801 (PR)
Eligibility Date: End of April 2016 (Applied a month prior).
PR Granted: Early April 2017.