That is unfortunate. The good thing is, Kiwis are friendly and helpful so I do not think she would have much trouble.
She'd probably need to get a warm vest for winter in NZ. I can't imagine it being easy to wear anything with sleeves when you have a cast on your arm.
A camera with anti shake feature would be required, so one handed shots don't end up looking blurry. Using a sling handbag/pouch would probably be easier than a wallet.
As for luggage, pack light, especially if your sis will be moving around the country, as most travellers to NZ do. I find 2 wheeled luggage easier to manage on slopes and gradients than 4 wheeled ones. The 4 wheeled ones tend to spin out of control.