Well if the Duke is ruthless in battle/with a sword, his future wife is sure as heck ruthless with her words!
But to point out about the shop girl that called MC out for not wearing a corset - i think she phrased it like she was saying MC needed a smaller waist, or "broken waist" (i think broken ribs when I hear that), but she was really calling MC out for being from the countryside/a commoner/unrefined - even though I'm sure the shop girl is too, just from the capitol - and trying to...subtly put MC in her place.
MC was not going to take that, from that girl or the tailor. So she destroyed them. No doubt to send a message to every other tradesman that she was not to be messed with.