Pre-paid debit cards usually work out extremely expensive. It's simpler just to take an ordinary bank debit card with you. As long as it has either the Visa or Mastercard symbol on it, it should work almost anywhere in the world.
Some banks don't charge for using a debit card abroad. (e.g. Nationwide's FlexAccount). Others do, but the charges usually come to far less than alternative methods of getting hold of cash. However your friend should notify her bank that she intends to use her debit card in NZ, otherwise she might find that the withdrawals are treated as 'suspicious'.
Chris