If you think this is absolutely insane, it is! But, Charlotte has her reasons for it. She knows Lizzle is being abused at Bachoff by Anton — just like she was years ago — and wants to stop it. In an effort to save Lizzie, she realizes that if she’s missing a hand, she can’t play the cello and keep performing for Anton. Lizzie (along with the other girls) has also been brainwashed by Anton, and as Charlotte explains “I knew you weren’t going to leave without a fight.” The only way to really rip her out of Anton’s grasp is to literally remove what she needs to play. Her hand. And the only way to get her to do something that drastic was with the help of an hallucinogen.