She antagonizes everyone in their first meeting, and I do mean EVERYONE, who is named or looks even vaguely important. She'll always have something tactless, arrogant and provoking to say. She is bewilderingly NOT clever.
She accidentally falls into the ML's healing pool in ch 01. She incapacitate the ML and immediately thinks to sell him for money. Doesn't come up with any other less unsavory scheme or asks him to help her, nope.
Later she'll have the audacity to be angry at the ML when her royal brother promised to return the 3000 teals to ML. She'll scheme to steal it back. This is the amount she made from selling the ML after he semi-publicly called her out, demanding the money in a meeting filled with very important dignitaries and high ranking foreign royalty from every country surrounding hers and this nation's.
She doesn't remember she's in the body of a foreign princess on a diplomatic mission with her royal older brother. Doesn't even consider that even if she manages to run away from ALL the prince and royals she effortlessly and pointlessly offended (Except the ex fiance, fuck him. He deserves her humiliating him.) that if the entire damn continent erupts into war due to her stupidity she has no where to hide and seek safety.
A few chapters later she's wandering around in this nation's palace lost, trying to escape with zero pre-planning or even a crude map to point the way and accidentally meets up with its king...while he's bathing. 🙄😒 She immediately gets aggressive and attacks him despite being the one intruding on HIS private time in his own damn palace.
She has no other plans but to attack relentlessly, recklessly and cluelessly. That's it. That's her personality in a nutshell.
When assassins were sent to kill her (not by the ML or the King though they'd be thoroughly justified) she somehow persuades the ML to kill the assassins with what looks like VERY recognizable, unique hairpins she has ML use like secret weapons. Of course, this plot hole isn't brought up again.
Her royal and very loyal brother is also equally stupid. He should, of course, defend his sister and always have her back no matter how rude or illogical she is but by calling out the other dignitaries' and royal's ugly behavior towards her he completely ignores everything is own sister is doing right in front of him and them. There's no plausible deniability for him so I don't understand his audacity.
All of this within 35 chapters.