I am one of those folks who can't visualize the end product. Your customer may very well be the same way. In my case, I would appreciate a "mock up." It can't hurt to try, but the final decision, of course, will be hers. I think you are a very thoughtful quilter to be wanting a happy customer in the end. Imagine how bad it would be if she hated the end result and you hadn't shown her a "mock up" or expressed your concern?