Why does Helen's family let her get away with her impertinent manners?

Helen Keller's family lets her get away with her rude, impertinent manners because they simply don't know how to handle her or teach her. She is blind and deaf, and they have not had any training with how to deal with this. They are aware she is frustrated and that she is having increasingly frequent temper tantrums, but they just don't know what to do. They love her, and they don't want to become intolerant of her.
However, the parents don't simply sit still and let this behavior go on endlessly. They do seek out help for their situation, and this is how they are able to be linked up with Anne Sullivan, who has the training, patience, and temperament to deal with a child like Helen.