Have every sympathy as went through much the same thing as a Saturday girl in a shop. My manager was obnoxious, took excessive breaks and was just horrible to everyone. The only way we got rid of her was when she was so rude to a customer, the customer somehow got hold of an area manager's home number and rang that person on a weekend. She was sacked very, very promptly. Maybe you need a friend to pose as a customer, who needs to complain to the manager, when the manager isn't there as she's having her nails done, and as her complaint isn't addressed, she then takes her complaint further.
Not a very good solution, but I wish you all the best with this one.