Look, there is no way it can be illegal for someone to wave a knife around in their own home. I don't care what the law says, if the law says you can't brandish a knife, why don't they just ban knives?
The law is bad enough over here. Can't carry a knife for self protection, and we wonder why people are attacked and robbed. They can't fight back, obviously. Some demented people here even ask 'why does anyone need to carry a knife'. Well, duh. Most people carry a knife for self protection. I wish I could.
As has been pointed out, the view expressed in the OP is wrong. It's not illegal. She's on private property so has not broken a law there, and the possible charge of assault would not stand as she's defending herself, her property and her child.