Easy,
Your story really makes me cross, particular the attitude of your customer!
I would probably lose sleep over this, let it really wind me up, plan lots of vengful attacks; and then do nothing.
I think you've got to write this one off; put it down to experience; bill it to the tax man and try to get a decent nights kip tonight.
She's the idiot, not you; you sound far too level headed and 'nice'.
It's her loss mate.