
In your position I would get together a FACTUAL report of your girls condition (History, Vets reports etc) and send a copy to the Kennel clubs Health and Genetics Co-ordinator Dr jeff Sampson, and also one to each of the Breed Clubs so that they can look into the matter, and decide if there is an inherited health issue to investigate.
Sadly this will not prevent her breeder breedeing from or registering offspring from her sister, but one would hope that the y if reputable and concerned with the breeds welfare and health would choose not to do so.