The gown has been washed ?. I am thinking of a product used in machine embroidery. It is wash away stabilizer. I am wondering if you could put your markings on this stabilizer, baste it to your gown, do your embroidery and then "wash" away the stabilizer. Anyone done something like this? I would just use a light #2 pencil I think for the marking on the stabilizer. I would also try this on a scrap first. It has been years since I have used the oesd Aquamesh product but to dissolve it, you just soak it in warm water and rinse.