Hi June and Joyce,
I would tell the customer to get and use a dust ruffle when using this quilt. Since it appears that you made the quilt according to the customer's instructions you did what was requested. In this case though the customer did not have clear instructions. She should have included a total size of the quilt for you before you started. You could have clearly determined then that additional width would be needed for sashing and the borders.
This is a case where the customer should learn by her lack of thought prior to having the quilt assembled and hand quilted. She should have made sure she was going to have enough of the quilt to hang down on each side of the bed for what she desired. This she clearly did not do. I would ask her did she measure any of her other quilts or bedspreads?
Hand quilting the assembled quilt and binding has been a lot of dedicated work to complete. I'm not sure what you charged if anything but having to undo the binding and increase the size of the quilt is also an enormous task. I'm not sure I would want to tackle the job. I would want to determine if adding the additional borders all around the quilt top would in the end look like a second thought to the quilt. It can be done but doing so would need to be your decision alone.
If you are not sure that you can remove the binding and add to the quilt and still have the quilt look and still keep the integrity of your previous work then I would probably not attempt the task.
Good luck as you make your decision.
Pam M