fierymagpie

That's the reason why she accept the marriage because she has no power, no friend and no money, as long as she became the fiancee of the CP, no one in the house could retaliate against her, they couldn't lock her up or hit her no matter what she did, beside what else she is gonna do, let them be like the OG did? Whether she is being polite or a bitch, they hated and mistreated her anyway, acting cute won't help in her case. about the sword, in the modern world she won a medal for fencing, she also learns kendo, so at least she knows the technique, it just her new body isn't used to it. it works against the bullies because they are just 'bullies', she won't stand a chance fighting against a knight, the Duke also see that she is 'lacking' thus offered to train her, he compliment her simply because no woman ever interested in swordsmanship nevertheless hold a swords

(1) The FL knows her limits that's why she acts the way she does. She's powerless i that house in the way that you're thinking but she isn't like utterly useless otherwise it would be a lot worse for her. For one the marquise cares a lot about reputation so she uses that as leverage bc no one outside of their home knows about how she's treated. That's why the prince was so shocked to hear about her saying his goals align with her's...bc his goal is to take down the marquise. He has never given her any type of education and allows his children to abuse her. Another thing is that he NEEDS her in the same but opposite way that the crown prince needs her. The marquise wants to use her to marry the crown prince and then take out the imperial family BUT the crown prince wants to use her to marry her and take out the marquise. He can't use the other girl because she was already married and divorced so the only other girl he can use is the FL. He needs the FL to achieve his goal. That's why he panicked when she stabbed herself bc if she gets injured or dies...his plan will fall through. She's not completely powerless and she knows this which is why she acts the way she does. That's also why she agreed to the marriage with the crown prince. That title will give her more power AND she wants to help him take out the marquise. There are some more things I want to say but they are spoilers and for that reason I will keep them to myself.
(2) She wants to practice wielding a sword in this new body but she is already trained which is why the ML was surprised to see her skills. She took a BUNCH of different material arts classes in her previous life and she also took classes learning how to wield a sword. She doesn't magically know how to wield a sword bc she already knew. The reason she wanted a trainer is bc this new body is much weaker than her old one so she wants to get better at it in her new body. You might've missed/forgotten this but in the beginning it showed her with all her awards for martial arts and stuff.
I'm not trying to invalidate your opinion in anyway so don't take this the wrong way. I just felt like you may have misinterpreted some things or forgotten certain details.

Sorry to say but I think you just didn't follow it properly. Two people already explained it so I won't repeat but they give a reason to everything, you just some how forgot or missed it? Like they literally show her in a kendo uniform inthe first chapter and she says shes only engaged to get power multiple times so...yh....thats on you for not understanding

Where did you read the novel? I didn't Knew there was one

I didn't.