This was another super interesting chapter! I am frankly almost amazed at how unclever Mielle is. Her nanny basically spoonfed the idea to meet lower rank but up and coming people since she couldn't go whine at Isis about the broach. On top of that she really has no clue about any kind of lifestyle aside from her own, nevermind the fact that maintaining a noble or aristocratic household isn't unlike managing a business... Considering the woman seemed to be a commoner (or at least wife of a wealthy merchant) Mielle's apparent advice was pretty useless, particularly considering Mielle wouldn't have any idea on what it means to earn for oneself since she lives off her father, and would live off her husband on the future. Aria learned her lesson in regards to this since she's lived at both extremes of the wealth scale, but also has the hindsight of getting a do over since she knows that she can't reasonably rely on anyone.
And once again, Mielle is parroting Aria and failing completely because she doesn't understand what Aria's purpose and intent are in those actions. Like, the whole gift giving thing in general. Way at nearly the start of the story Aria gave embroidered handkerchiefs to the ladies at Sarah's tea party right, despite know she wouldn't get a whole out of it right? The difference then vs Mielle now is that 1) the were handmade by Aria and it's hard to refuse something someone made themselves vs something bought from a store (and I doubt Mielle is creative enough to have designed that rose broach beyond asking for it to be a rose and that it should be shiney) and 2) if I recall correctly Aria made them so that it had the lady's family crest/emblem so it was also personal to each of them. Aria may have been doing these things to improve her reputation but it showed thoughtfulness on her part.
Then if we compared Mielle's broaches to Aria's... Aria gave them to her maids who had been working for the family, so having something that represents their employer kind of makes sense? And since she chose a design that's more simple and elegant rather then ornate and flashy it means the broach can be worn more often with a variety outfits. Mielle's on the other hand end up looking like a flex on these women whose social and monetary rank are lesser then her's, plus by using an emblem of a family that they seemingly have no connection to, the broaches kind of read a bit more like a fanclub badge that no one asked for. Unlike Aria who has earned over time various people's loyalties, Mielle seems to just expect it because she's always had it by association.
If Mielle was even slightly smart, she'd be writing to Oscar letting him know in veiled words that she's aware of his feelings towards Aria and that she feels bad and that he should feel bad that she feels bad. Then she should have at least offered to put in a good word to her father about investing any expansions that any of their businesses might need in the future (not that it would mean much since the man doesn't follow any of Mielle's suggestions anyway but the women don't know that) and finally really played up the fact that she got those broaches especially for them and that she wouldn't give something like that to just anyone... So that they would take it even if they could never wear it (and then, idk, plan an opportunity for them to wear it and favor the ones who do over the ones who don't.)
I also suspect that had she stayed and not rushed off when they either wouldn't have invited Aria or invited them both. Mielle leaves this chapter with basically no meaningful connections and a bunch of tacky rose pins. And Aria's circle of allies seems to get bigger...