Nature's Miracle is good stuff. Got my dog to forget a few of his "favorite" spots when he was a puppy.

Is it possible she's having some trouble, and not just that she's found a nice handy spot she doesn't want to give up? If she's having a problem controlling herself (my old rottie did, and I don't know if it was the rimadyl that did it but it happened at the same time) maybe put some x-large piddle-pads down for her?