It's her net shawl that gives the appearance of a bustle but the lines are still triangular rather than squared
If you can get your hands on bridal tulle, the very soft stuff for veils and gown overlays use that. You can embroider net and tulle, and the stars are fairly self repeating. Use silver embroidery thread and then if not enough sparkle add beads, but start with the silver and add the beads. Silk tulle, which this would have been, does not hold hup well to weight of that many beads over time
Also the painting suggests the silver is embroidered, so the tulle may well be the over lay not the source of the silver. The skirt definitely has an overlay of plain tulle vs the bodice where the silver is much brighter:
Good luck and great taste!