
She already have money
She already have support of her uncle
She got her mana back
She knows that marriage with Duke can be potential red flag on her surviving
Although it's Duke who should be more in marriage he left all problems to deal with his family to her ( he basically doing nothing or barely minimum)

But she knows that if she doesn’t marry the villain the story will go on the original path so she may be walking into a lions den but she needs an ally to protect her from the male leads and other nobles due to the rumors and the male leads also may have a higher status than her so she could also be pressured by society to not say no to them because she isn’t as high standing as them.

I did it because document is fake but I can't prove it that is fake ( seriously this is your defense). We have him alive so we can use him, no you can't die ( letting him keep weapon and talking how they will use him in front of him). Where is a father of her? King who is giving documents to translate to some girl knowing that it's his daughter scam but behaving like naive noob when matters of his kingdom are in full blast)

I am just on 13th chapter but solution of her " wearing the same problem is so obvious that it's hurt to read it again and again" Change tailors, change servants or choose outfit for the party in last possible moment so information about it won't leaks. It is obvious that someone is leaking information about you and this is what you should solve first

Don't forget, the bully has money, power, and parents that don't care what she does. She's better off identifying the spies and using them against the bully, especially since any new staff that come in could be sus too, she cannot trust anyone at this point, except her family and fiance. She would be better off cashing in all of her lottery tickets and escaping (on foot) to the mountains as a sheep herder.
I don't know who she ends up but for me the only good ending would be if she was able to bankrupt black hair guy, made crown prince a laughing stock. Her ex husband didn't do her any harm and paid her high alimony without lawyer involvement but from other side he was extremely stupid ( believed in all lies about his wife) so he deserves to fall in love with her and get rejected any other ending would be bad ending as man here are too trashy to be considered as a ml.
Best they all bankrupt and die e.g during world war one.
I’ll be dropping but this was the best ending and only one for me