A dust ruffle will only work if the quilt already covers the mattress, which may not be the case. I would go over the other options with the client, pricing them to cover my time and materials. It might turn out that the client decides to keep that quilt for another bed (or to give as a gift) and asks you to make another quilt for her bed. In that case, be sure she provides good measurements, realizing that the quilt will shrink a bit when quilted.