She look slovely. But, I'm going to take a wild stab in the dark and guess that she is here on a working holiday visa. Make sure she still has work time on her visa and therefore you can hire her legally.
BTW, there is no legal minimum wage for a live-in employee.
I have heard good things about kiwis and ozzies. I was thinking I might go down that road for my next nanny.
If you are paying for two kids to go to nursery full-time I would think the nanny option is within reach financially. So, you must be forking out some £1700 per month. That's £392 per week. And they don't do laundry.