The answer is actually quite simple: they wouldn't take any of it off.

Pantlike underwear was only gradually taking hold in the early Victorian era. We simply don't have the sources to know exactly how many women were wearing drawers (an undergarment, generally of white cotton, made like a pair of capri pants with separate legs and an open crotch) at the time, but it was a minority: most women wore just their chemises, corsets, and petticoats instead. And why not? No wind was ever going to be strong enough to blow all of that out of the way and embarrass you in public, and using the chamber pot is quite simple that way - just get it underneath your skirts. It was not until the popularization of the hoop skirt, or cage crinoline, in the late 1850s that drawers really became a necessary item, because the hoop made the possibility of exposure much more likely. It could be caught in the wind, or get stuck on a piece of furniture, or fly up when you fall or bend over ... drawers were not terribly flattering, but in conjunction with a short underpetticoat, they would save your modesty. And as I said above, these were open between the legs, so that the same process applied: just get it underneath your skirts and kneel over it or sit on it. It's not until the 20th century, after the Victorian era, that closed underwear became the norm.

That being said, Victorian women's clothing was really not that difficult to move in and did not consist of that many layers. In comparison to today? Yes, there's a lot of clothing. But it's not as though women were prevented from moving around. The lower half of this dress is not an upholstered piece of furniture, it's a skirt and petticoat (or two) draped over a wire frame. Women went hiking and riding in fashionable dress made out of durable fabrics, and later played tennis and went bicycling in clothing with only a few design changes to facilitate the activity (e.g. divided skirts).