I find no issue with her. You guys are just unnecessarily hating on points that you'd be fine with on any other character at this point. Obviously she has her flaws, but that doesn't make her annoying.
I'm saying this as the translator, so I spent quite a bit of time with her lines and character, still not annoyed of her.
Personally I don't particularly hate her, but I acknowledge that the way she's currently been written is far less sympathetic than the other 3. Objectively the female half of the quartet has been given less personal growth and development(or change)at this stage, and in Mari's case a much more entrenched and self-centered mindset. In contrast to Seki, who's "doing all he can" and doggedly focusing on winning Mari, and Pon, who goes Rocky training montage, they're a bit more stagnant. Kon has decidedly shown some depth, if not "progress", but Mari has only had her "issues" highlighted for the most part. There's probably some projection for how quickly she "wrote off" Seki and decided to find someone else, that can certainly give some folks a negative opinion, which is fine.
All in all, I think it's far too early to write her off, and still currently easy to make her sympathetic, if that's what Aka chooses to do. 🤷♂️
Edit: Oh, and nice work.