What is to be done about my wicked sister?

It is obligatory for you to prevent your sister from corruption using the most appropriate method, which varies depending on individuals and circumstances. If shunning her leads to her righteousness, then shun her. If drawing close to her and treating her with kindness is better, then do that. Use various da'wah (invitation to Islam) methods with her, along employing kind and gentle words, and supplicate to Allah for her rectification.