First, fashion is a nebulous thing. We don’t buy a whole new wardrobe whenever a new style appears. Some older pieces often remained in a collection because many things had to be handmade, either by you or by a seamstress. The style at the time involved a lot of layering. First, women would wear a chemise under their corsets. It was like a long, fluttery shirt, often with embellished straps, as you can see above, or light/no straps for the evening. It protected the body from the corset and was far more easily washed than the corset.
Most of the corsets of the time stopped below or mid-bust, meaning that some women wore brassieres for support, though some didn’t. What Rose appears to be wearing here does cover the bust, so it might be older or just a different style. The corset itself wasn’t laced super tightly around the waist. In fact, at this time, it was more to slim the hips for the new, more slender skirt silhouette.
That chemise we are seeing on Rose might have actually been a combination, which combined the chemise and drawers or knickers, which were leg coverings with a split crotch for bathroom use. (Separate pieces and combinations were both used in 1912.) Then you would have a corset cover garment, which would smooth out the lines and was often embellished with buttons or ribbons. You might also have petticoats over the whole thing, which were decorated at the bottom and often had some flounces. Then the dress goes over that. Not convenient if you’re in a rush to pee.
It’s complicated, especially if you want to stay hydrated during a shoot. Still, the attention to historical detail is wonderful to this history nerd.