Dresses were very expensive in the past but for a party with fancy food and venue I think of this
First thoughts as a rich daughter betrothed to royalty: Let's clean up your dress so you can use it many more times, let me wash it with my pleb-like knowledge I learned from my mother
Girl with dress: (Her mother acts like that? She repeatedly used the dress instead of buying new ones even though she is engaged to royalty?)
Lately all the shoujo I've been reading are fantasy-isekai, though I really love those I wish they also put a few more historical (no martial arts or magic) ones on peasant, non-royal affiliated time-traveling girl (sengoku komachi is close but nobunaga is kind of royalty)