First of all,
Big mouth forced our MC to suicide if not DK; then it has been showed she was a dick and bully to our dearest Kindra and on top of that she thought she was helping to her in her deranged way; she basically used Nicholas to achieve her goals in TWRR; after everything happened she had the guts to blame MC for everything she did and even implied he deserved it; after that she sent people after MC and Kindra; she lied about MC and blamed him and Kindra for stealing and if not Kindra at a public interview, she would have publicly execute MC's and Kindra's credibility without even having second thoughts; she fucked over Reina and her company for her own fuck ups and caused multiple people fired from their jobs and also caused huge dive for Vitas(Reina's company) in the market; also caused entire HR department at TWRR to their job and she dared to mock them while the person who just got fired presence; then simply threaten Reina for more just for getting MC's phone number; she also sent people with guns to break in Kindra's place; she fucked up a child's mind for the sake of it within a few seconds she met her etc. She never showed remorse, she even thinks she is the rightful one.
Vader was always remorseful about his situation, he made mistakes and owned them. Even though he was a feared person, he did not commit unnecessary evil. You mentioned younglings, it was an order for him and also a test for choosing dark side. He could have done so much more, could have turn into real Sith Lord but he did not. Don't get me wrong, I am not trying to justify what he did but we are comparing an evil villain to Big Mouth and that evil villain comes short in his evilness in their own capabilities. So, what I am trying to say if Vulvamort had Vader's abilities and power, she would have destroyed galaxies for the sake of it. She would have been perfect apprentice for Palpatine.
All in all, some people are beyond redemption and that is that. Maybe she could have justify how she was with some childhood trauma but no way bring back what she took from people. Btw, I can see they are gonna explain her evil self with her father and her relationship with her father, I am sure of it. Especially after the lab scene after she bullied Kindra and MC wanted to meet her father.But,
