I have had one of my Ragdolls not take the first time, and typically I don't breed a queen the first time until close to 15 months. The second time she took and had 4 healthy babies. I just don't think she was mature enough at that time, but proved to be an excellent mother.
However, I have had a Ragdoll that I tried many times to breed, and she either had false pregnancies, or she was absorbing the kittens early on, and she had to be spayed and is our pet.
In my opinion, I would only try breeding the queen 2 times, and if she isn't taking, I would spay.
Some breeders, I would say most breeders have a clause in the contract regarding fertility, but I do know it will be dissapointing to you to retire her if it comes to that. Especially, since she has done well in shows.
I have found that Ragdoll females don't mind taking their time in becoming pregnant the first time, and know some who's queens were closer to 2 before they were really interested in breeding. It could be possible your breed is a bit slower in growing into sexual maturity.
We have a beautiful large male, that didn't become interested in girls until 2, and sired his first litter a little after age 2, but now that he has figured it out, he is a pro!