Tataritka

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.

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)