IF she is travelling as an infant, on your ticket, you can take it for free.

PLEASE!! I learned this the hard way - Qantas charge extra baggage per ITEM - not per weight. So you can pay for an extra 23kg, but it has to be in one bag - they will charge you for any extra bags, costs a FORTUNE.

So CALL them and do it all over the phone to get definite answers on the number of pieces of luggage and any additional costs. It will cost $20 a piece for the first 2 pieces, then something like $40 for each piece thereafter. Totally illogical, so CALL and get it straight before you get to the airport.