I would tell her that she must have confused me with the insurance company. And to refresh my memory on when and how exactly I approved a longer session and the charge? And then I would probably quit, unless she super super apologized for being an oaf, or said her husband did the billing and made a mistake or something. Unless you're made of money, this is something a client is very vulnerable about. If she says her computer was out of control or something, okay, but she needs to acknowledge it, I think.