http://www.hrmonline.co.nz/article/r...hr-141542.aspx
She can make a legal challenge against said company for withdrawing the offer.
Technically if she had a written offer, than an employer/employee relationship exists between her and the company, so at the time of travel, visa is still valid.
What has happened is other party has now terminated said relationship, so that person will be in exactly the same position of anyone else when their employment ends somewhere whilst they have an existing work visa. Unsure of this, but presumably conditions will be in the VISA.
Other area is grey really, unsure if she'd be given additional time by immigration to challenge the decision through employment tribunal; my suggestion would be though is she lines up exactly what she intends to do before chatting to immigration directly.