Hi Vee,
Mmmmm, difficult. She wouldn't be allowed to work on a Visitor's Visa so she would need a Work Permit. However, with a WP, as with a lot of other visas/permits, the employer needs to prove that a kiwi couldn't do the job over an 'outsider' and the job needs to have a skill element to it to qualify.
What would happen if she came over on a VV and worked for you on the quiet, I don't know, suffice to say, if you were found out, it could possibly have serious consequences. There's nothing to stop her going down there for up to 9 months on a VV, but working without a permit would be severely frowned upon by NZIS.
We had a lady on here a short while ago asking if she could bring her maid into NZ when she immigrated, but the answer was 'No', but that was on a permanent basis.
Thinking about it
, as she's under 30 years old, she could apply for a
Working Holiday Visa which does allow some work although the main purpose of the visa is for holidaying. She could get a 12-month one which should sort her out and seems to be her best bet.