As I noted in another thread about pooling frequent flyer miles, Qantas does not allow you to accrue to a shared account, but does allow you to transfer miles between family member accounts.
Family transfers enable you to transfer a portion of your points to an eligible family member, who is also a Frequent Flyer member, up to four times in any 12 month period
What you would do is have your wife open an account in her own name and assign that number to her ticket. After her travel is completed and the miles credited, she should be able to log in to her account and initiate a family transfer, or request one with a phone agent (for a fee).
See Terms and Conditions for restrictions. "Eligible Family Member" is currently defined as
Husband/Wife, Parent/Step-parent, Domestic Partner/De Facto, Child, including foster & step-child, Brother/Sister, Half Brother/Sister, Grandparent, Grandchild, Son/Daughter-in-law, Brother/Sister-in-law, Father/Mother-in-law, Uncle/Aunt, Nephew/Niece, First cousin