Yikes! The fabric is already being used? She could try washing the completed quilt in Retayne to help set the dye, however I have only used this product when it is still just fabric yardage never in a completed project. Maybe throw a shout color catcher in as well to keep the bleed from going on the front of the quilt.
If this is a wall hanging, perhaps it would be best to just live with the dye coming off during quilting then put another back over the backing (like muslin) before binding it to keep the dye from transferring to the wall.