It's difficult to provide comprehensive information without having seen the orders.
What I'm gathering is that your child lives primarily with your ex and her husband and spends time with you, and I assume you share equally in parental responsibility.
If this is the case, the mother cannot move without first consulting and reaching agreement with you as a move from Victoria to Western Australia is a major, long-term decision about the care, welfare and development of the child, and I assume it will also significantly impact your child's ability to continue having a meaningful relationship with you.
Further, I assume it will also mean the mother is unable to uphold her end of the orders.
If she relocates without your consent, you can file for a recovery order that would see the child returned to your care, potentially by ordering the mother's relocation back to Victoria. The strength in your case would be in regard to the significant impact the relocation has on the child's ability to have a meaningful relationship with you.
It may also be necessary to file an initiating application to change the current orders as the circumstances have changed significantly. Changes might include all holiday periods and one or two weekends per school term, or it might include the mother paying for all flights to facilitate the child spending time with you.
I would get legal advice for this matter, but I hope the information I have provided has in some way helped.