MikeB4:
@networkn I think Rob Muldoon, Geoffrey Palmer and Mike Moore still have the lead for that title but she is closing the gap fast
Interesting element to that comment... two of the three names on your list were only PM for a brief period (less than a full electoral term) following the resignation of a Labour Prime Minister.
If Ardern were to resign, then Kelvin Davis would become Leader of the Labour Party (and conceivably, PM*) and he would almost certainly be rolled in short order by either Robertson or Andrew Little, which could see history repeating itself.
*this would depend on the (supressed) detail of the coalition agreement though.