She should have done the math- plain and simple!! The only safeguard in the future is to give a written rough estimate and have the customer sign the duplicate copy. Make sure they get a copy. At $.01 an inch, she got a "DEAL". I hope that in the future, you will develop a LAQ checklist that will state backing requirements (will be returned unquilted unless the backing is at least 4" wider on all four sides), threads clipped, .... This could be emailed to customers or just signed off on by customer at the drop off of 1st quilt. Some folks are just plain difficult so please put this experience aside. We can't please some people no matter what!