Wow, from everything that you just said, it sounds like the "breeder"
is willing to say anything to get those pups out of the door. She obviously lied about the weights of the parents and the whole thing about the tails being naturally short and them just not having dew claws is outrageous! If she is willing to lie about things that you can very easily catch her on, just think of the health problems she may be hiding!
I would definitely suggest that your sister hold off. I know that can be hard when you really want a puppy, but it is so much better to wait and get a healthy pup from a breeder that you trust!