OK, a couple of things here, and excuse my skepticism, but I think you need to seriously question what has happened here.
Accidents can happen but... I would find it very, very difficult to understand how a reputable, care-focused breeder could possibly have had a pup left alone in the house in such a situation that it could have broken a leg with this severe type of break. What could a pup possibly have gotten caught in that it would have twisted and snapped a bone in its leg? Where were the pups being kept while they were being moved? Weren't they safely in crates; or penned; or were they running free inside, which to me, doesn't sound like someone who is very experienced at breeding and managing puppies?
Anyone who has had puppies here would know that they are pretty robust.
That's why I'd be really dubious about this story and be wondering about the breeder, especially if they are not a reputable club affiliated show breeder. I would just feel there's some other story behind this break and it probably involves a poor duty of care. This type of fracture is generally due to severe force... The pups I know of that have had leg fractures have had them because them jumped from a height or fell or something fell on them. How could a breeder first not have them in a safe place to start with,
especially when they are not being directly watched (that's like leaving toddlers running free in the house while you put some other kids in the car; you simply would not risk it!!); and second, how could this happen and the breeder not know what happened?
And what does she mean by 'it hasn't affected the growth plates?' A break is a break. If it is pinned properly it will heal but may require a permanent plate to bind the bone shaft together.
Even with the very best of breeders, I would not take a puppy that had a leg fracture unless I was prepared for future problems; I'd want to confer with the vet; I'd expect a very low price (if any at all) for the pup because I'd now consider this a special needs dog with potential for future problems.
Unless this is an exceptional breeder, I'd be looking for another breeder and another puppy. Her explanation sounds suspiciously fuzzy to me and I'm a bit taken aback that she would still be considering homing the puppy as if it were a normal situation, even assuming it heals well (and it will be several MONTHS before they would know this! How can she possibly think it is a matter of a couple of weeks?).
BTW this is a vet's response to someone whose puppy had a similar break:
A spiral fracture suggests a strong force was applied to the leg. A dog cannot apply this much force to themselves, the nail would rip out before the leg broke. In children this type of fracture is considered classic for child abuse.
Depending on the severity of the fracture, a bone plate might indeed be necessary. A simple mid shaft fracture might be splinted or casted, but there is not a lot of support from the fibula bone to stabilize the area. Often the fibular is fractured as well, but usually repairing the tibia is sufficient stabilization for the fibula to heal.
At the very least, a consultation with the surgeon would help determine if a bone plate was necessary or another procedure might work. Also, with recurring bandage or cast changes, the total cost of a fracture repair might be the same, regardless of plate or cast.
Elsewhere, vets note that such a fracture may indicate underlying weakness in the bone to start with, eg indicating there's some problem already that caused the fracture. Either way if I were a breeder I'd not be homing such a pup for a good long while until the situation was thoroughly evaluated and I'd be homing it in a rescue context, not selling the puppy.