I bought this one of a kind outfit for a pretty penny from another collector. The seamstress is unknown, but the quality of the gown is amazingly detailed. The seamstress added a generous amount of lace detail, including an attached lacy petticoat that gives the dress its fullness. The white fabric feels like taffeta though I'm not 100 percent sure.
Attached petticoat has generous lace trim that helps give the gown its fullness: