I love it, so many of these villainess stories are so blunt and heavy handed with insults. Even if they were a bit too direct and hostile it was a good exchange.
(I'm just gonna ramble and point out the obvious from here on out.)
So the pink haired girl says that the mc has worn the same dress 4 times, and that can only mean one of two things: She doesn't have money (which no one would think is the case given her family's position), or she is too unfashionable for polite society. The mc then pulled the piety card by saying she was plain. She took a loss that wasn't really a loss as modesty is as much a virtue as low self esteem is a flaw. She then complemented her antagonist (which makes the pink haired girl look like a jerk), then established the quality of the dress. By pointing out that the dress is of high quality, the mc proves that she has fashion sense which negates the original insult. The pink haired girl accepted that loss in exchange for the prestige of having her own tastes and wealth acknowledged. Then, with the pink haired girl's confirmation of the quality of the dress the mc proceeds the wreak the girl's social standing by revealing that her parents are desperate to marry her off to a rich man before they collapse financially. I imagine she uses some of her future knowledge on this one. If for no other reason than it is information that pertained to one of her early rivals in her previous life, she would have likely noted it and remembered.
If I had a complaint about this scene it would be that she acts like an injured puppy when the Grand Duke appears, and the pink haired girl loses all composure. It can all be reasoned though I suppose. The pink haired girl just received a shock and would like to take the opportunity to get on the Grand Duke's good side since he appears at social events so infrequently. Still, she assumed someone of his standing could only be coming to talk to her and deserved to be brushed off, then she got right into his face and demanded something of him at the end. Not the way a noble lady should act at all.
The main character's puppy attitude though is a bit harder to nail down I suppose. She's supposed to be quite smart so on one side it's possible she's trying to act the way the she thinks the saintess would act. On the other hand it's possible that she's just tired, uncomfortable in the spotlight, and appreciates the attention after being emotionally abused by her mother her entire life, then betrayed by her brother.
I hope the story continues like this. I've always enjoyed trying to pick apart human interactions.