Proceed through the booking process as if you were actually going to book. Pick your itinerary (4 night cruise only) your dates (1/25-1/29), number of people, stateroom cat., etc. When you get to the end, you will receive a quote for the cruise showing your total. Look a little further down that page and you will see hyperlinks where you can change whether or not you want insurance or transfers. Look a little below that and there is a line labeled "Booking Code" with a hyperlink labeled "Optional". Click on the link and a pop up window will open with a box where you put in code "APC." Then it'll ask you where you got the code -- doesn't matter they just want to know for research purposes. Choose one and then tell it submit or OK and it will close and your adjusted price will appear on the quote page, if the room category you picked is still available at those rates. If you don't see a discount, try different room cats.
I'm not 100% sure about your daughter, but I think the cruise is different from the resorts in that all members must have an AP to sail, whereas at the resorts, only one must have an AP. Before you book, I'd call
DCL and ask about this and make sure it's possible for the rest of you to get the discount, even if she doesn't.
For what it's worth, I used
Dreams Unlimited travel and had no trouble getting the discount applied, plus they gave me an instant rebate, resulting in a fab rate.
JD