@XieShu Some people's anger boils like fire, other's fester like untreated wounds.
She is definitely angry, but the type of anger that just drains you of your energy. Not to mention that she lost her entire family to the person she loved (and that said person had lied about pretty much his entire life). She is DONE with everyone's bullshit.
Also, in a sense, her actions were a giant middle finger to the guy. "Oh, you want me to live the rest of my life in a monastery, how kind of you! (not really)" Nevermind the fact that the people of the fief wouldn't be satisfied with that. They were out for blood. She would have definitely been assassinated at some point by some crazy guy with a revenge boner. Putting herself as the villain and getting executed would cement the guy as a hero in the eyes of the people, and provide her with a quick end. Except he wouldn't be a hero: he would be just another revolutionary.
Sometimes, kindness can be the best revenge. And she didn't have much to live for, anyway.