Is Cadbury actually "in heat" yes I know rabbits do not have estrus cycles but rabbits will sometimes not be receptive toward the male at different times of the year or even different times of the month. There are a number of different methods you can do to try and get a doe into "heat" I like to let the buck mount the doe a little, and then an hour later I will put them back together. Rabbits are induced ovulators, so a doe will release an egg after the buck has mounted her, and it is believed it takes up to an hour for ovulation to take place. sometimes taking does to shows or places where male hormones are high will help bring her into ovulation.
My advice is to keep trying the one hour method, instead of just putting them in a cage, bring them out to a table and hold the doe still so the buck can mount her. By letting her run around or fight the buck gets worn out and may avoid her rather than try to breed her. Keep trying, unless she is truly sterile, she'll ovulate eventually!