
Well done for getting the health testing done.
She is too young yet for a litter, leave it another year when she will be 2 1/2, - 3, that is quite soon enough for a large breed bitch.
I have a medium size breed and our breed clubs code of ethics state bitches should not whelp before two years of age (what does your breed club/council advise?). In my experience mentally they are very much puppies until at least two years of age.
Has your bitch been doing well at shows, trials or other work? Has she been assessed by independent knowledgeable judges as being of the construction and type to be bred from?
If not then the next year you can prove her worth. Then you can start putting the word around in breed publications and at breed events to let people know your planning a litter. A lot will depend on what the main purpose of the litter is, are you breeding for puppy worthy to show, be a working dog, or Obedience etc?
It is best to have a good waiting list in advance of mating your bitch, at least 6 - 8 in a breed like yours as some fade away by the time pups are on the ground.