Quickly, Halsbury sums the position up at Conflict of Law Vol 19 as follows at :
"345. Abandonment of domicile of choice.
A domicile of choice can be lost by abandonment. This process is the exact converse of its acquisition. It is necessary for the person concerned to cease to reside in the country of domicile, and also to cease to have the intention to return to it as his permanent home http://www.lexisnexis.com/uk/legal/#ref68616C735F636F6E666C5F3538_1 1. Absence without the intention of abandonment is of no effect http://www.lexisnexis.com/uk/legal/#ref68616C735F636F6E666C5F3538_2 2; nor is intention without any actual change of residence http://www.lexisnexis.com/uk/legal/#ref68616C735F636F6E666C5F3538_3 3. Both the intention and the act must be demonstrated to be unequivocal, though the evidence necessary to establish abandonment is less than that required to establish acquisition http://www.lexisnexis.com/uk/legal/#ref68616C735F636F6E666C5F3538_4 4."
Note that merely leaving as such is insufficient, the term “abandon” requires that the individual has to leave with no intention to return to it as their permanent home. The matter was well summarised by Megarry J in re F, the Errol Flynn judgment. Whilst there is a bit of leeway between the Dicey definition and that proposed by Cheshire, there s no doubt that in your case, the lady would actually have to leave New Zealand with the intention of abandoning her domicile of choice, or of origin there.
Note that the post millennial HMRC have literally no idea, and do not wish to know what domicile actually is. They prefer to transliterate that into a new administrative law notion of permanent residence, which again is not the same.