Well, at least now you know that she and the buck aren't sterile!
I don't know where you are, but registration with the American Rabbit Breeders Association is only important if you want to show rabbits. Unfortunately, what makes a good show rabbit isn't necessarily the same thing as what makes a good breeder/producer, especially when it comes to commercial (meat) rabbits. I breed "fancy" rabbits myself, but some of the commercial breeders I have known have told me that the animals with the best body type for production would actually do very poorly on a show table, and vice versa.
But, back to the animals you are working with.
Did you check this doe before you put her in with the buck, or did you just put them together at random? A doe doesn't do proper heat cycles, but she does have times when her hormones make her more likely to concieve. If you use the same approach that you would use to check the gender of a young rabbit, and evert her vulva (can I say that here??!) a little bit, you can see what color it is on the inside. The color you are looking for is cherry red. That signals that her hormones are at their peak, and she is most likely to be receptive. Light pink says she's not ready, and a purplish color means she's past her peak. She may still breed and concieve on those colors, but your likeliest color is red. Some does never show darker than a deep rose color, but generally, the redder, the better.
When I have a doe that has lost a litter at kindling, I give her a couple of days to recover, then re-breed her. That is one of the highest hormonal peaks she will ever have. Even difficult does usually will be cooperative at that time, and concieve the largest litter that they are capable of carrying.
Joie, I think the fused pelvis thing is guinea pigs, not rabbits. I have had first time litters out of does that were at least 18 months old, with no problems (former show girls!) Particularly with small breeds, a doe that isn't bred young is likely to get fat, and fat can play havoc with the hormones involved in reproduction. Getting a doe back into production after a layoff can be difficult for the same reason.