I would do it after. You can use a ribbon as a guide by pinning at the sides of your pillow and then running your wheel along the edge of it. This way you will have straight lines. You can measure to give it consistent spacing or use a ribbon that is the same width as the space you want between the quilting lines. Then run your wheel along both sides of the ribbon and move the ribbon down so that one side is on an existing line and run your wheel down the other side.