The impossible dog to housebreak? HELP?

My first question would be have you had her to the vet to rule out any type of medical issues that could be causing this? If you got her from a responsible breeder inbreeding wouldn't cause that issues. A responsible breeder undertaking a line breeding that close would know the lines backwards and forwards. If it wasn't a responsible breeder no telling what problems could result because they don't know the lines. If you did deal with a responsible breeder have you spoken with the breeder? (Responsible breeders are always willing to be a resource to their buyers) They may have some insight on the problem. While uncommon yes mental defects can occur in dogs.