Anytime arrangements change, either parent can initiate a new evaluation as you are basically just updating your own circumstances. You need to contact Centrelink (pretty sure you can file new paperwork for this part online as you will probably simply be changing your FTB a/b entitlements) and the Child Support Agency, they will inform you of what forms need to be filled out and usually (has always been the case for me), things are backdated from your first contact with them (even if you need time to fill out the forms etc, they will note down the date you came to them and the forms will ask what evaulation period it is for ie. begining from a month ago, indefinitely) so the sooner the better. The forms include a section about the other carer's details (ie. her) and her end is then sorted out when she chooses to update her circumstances; you aren't responsible for her being honest but they will contact her based on the information you have provided so if she tries to falsely claim money it is going to catch up with her eventually, resulting in a debt so it is in her best interests to also update the information about her situation ASAP. I'm not sure what happens if things are not agreed upon and she tries to challenge your claims though as myself and DD's father have always agreed but I'm guessing it goes to some form of mediation where you demonstrate that he is indeed in your care for the time you are claiming.