Tapu Lei Lei

That dress looks absolutely perfect. I don't think you can do anything more to it to fix the clipping, so now try adjusting the model herself by widening her Lower Body physics body around her hips area past the boundaries of her skin until the dress flows past that physics body like it should - it'll look weird in the editor, but that should do the trick. My kawaii little Kimi-chan had the same problems around her hips with her Yukata (she has complete body skin under it), and that's what sorted it. Hope that helps.