Once you get into the system, you just need to have your daughter's iMIS number and date of birth. Then it's just a matter of confirming that you are returning to the same unit and paying by credit card.
For all of April, registration is only for girls returning to the same unit. That means your daughter's space is guaranteed until May and there is no rush.
As of May 4th, girls moving into new units can register as well. You will receive an e-mail from National to give you more information.