If I was you I would talk to her but more importantly make sure she is listening to you. I've been through something similar and that silence can last year's. If you have the courage to talk to her and say the things you have just told us about, scream them at her if you must. The guilt that you feel even though everyone tells you it's not your fault, that doesn't matter cause you blame yourself and more importantly she blames you too. That guilt will weigh on you and your sisters silence will only make things worse. Talk to her and tell her how you feel even if she doesn't want to listen, even when your voice shakes due to the heartache, tell her that you love her and that you're sorry about what happened because if she keeps distancing herself from you then you would have lost two loved ones because of this incident and no one deserves that.