It won't happen, and Mielle herself will commit more crimes and do awful stuff to prove she is a psycho pretending to be nice, and all because she can't stand being related to the daughter of a prostitute in any way or wanting power.
Her actions will lead to other people dying, she will ally with corrupt people, she will purposefully try to kill her own dad and blame the main character for it, and she will privately get mad that her father didn't die as it would have meant the money would get to her sooner, and she only complains once she is found out and gets legal punishment.
And even after being given a second chance with the MC acting nice and letting her be in her mansion rather than jail, Mielle will still escape and turn traitor to her home country, trying to court the royalty of another country while leaving the guy she said she loved behind now that there's someone more powerful near her, not only that, she tries to make it so that said country will attack and conquer her home country, and well...it seems like it will work that way but said royalty isn't dumb and doesn't actually want a war so he prepares a trap for Mielle and the other traitors and delivers them to the other royalty.
And they are all sent to be executed except for Cain and Mielle because the MC intervenes for them, although Cain has to become a severely supervisioned guard and Mielle loses her noble status and is forced to become a maid, to be fair, she is grateful at her sister for saving her after all she did, but she still despises being a maid and not being the head maid meaning she works for others, so with some slight incentive from the MC, she takes it upon herself to poison her new boss because she hated being ordered to, this fails and it's Cain who drinks the poison and after this, any good will anyone had for her is gone and we get a repeat from the start of this series, only it's Mielle being executed and the main character looking like a saint before heading to her and whispering how much she hated Mielle and planned everything.