OP, I think you will be fine, and I don't think Disney will give a Mouse's patootie one way or the other. Disney years, are not like our years. I think mastersd learned the same thing.
I took my nephew for his first trip in Aug. '08. He was 9 at the time. I took him back again in July '09 and he had turned 10 by then. While booking the trip, the CM wanted me to add dining. I told her several times that dining is not worth it with my nephew who eats next to nothing and needing the adult dining plan because he is now 10. I know I told the CM that he is 10 at least 3 times. Still, the CM kept quoting it with my nephew being 9 with the kids DP and ticket. Turns out, that since my nephew's first trip was in August, the Disney system doesn't age him up until August each year.
So, my guess is that in Disney years, your daughter will not be 3 until December and they won't look to sell her a ticket until then. I don't think you will be questioned at the turnstiles, but, if you are, I would explain about the APs and worst case scenario they will ask you to go to GR and buy a ticket. No biggie.
BTW it has been my experience that CMs don't ask age. I was on a trip with a friend and her 3 year old daughter. ALL 3 OF US HAD AP's. After Illuminations one night I planned on heading over to the MK for EMH. To my surprise, the little one wanted to come with me to ride the Merry Go Round

. Her mom was fine with that, but didn't want to come with us. I headed off to the monorail, while my friend headed back to the resort. After waiting about 20 minutes in the monorail line, it occurred to me that I didn't have the little girl's AP. No way I was getting out of line!! I called my friend, but she was already on a bus on the way to CSR. I decided to take my chances at the gate. I wheeled the stroller in without question.
Now, you may flame me for doing that, but I flame myself for keeping a 3 year old out until nearly 1 in the morning!!
