Puzzled, It sure sounds like you have been through the wringer. Many of us come from pretty broken families. It is so hard to grow beyond your own pain.
If you can, sit with the hurt, resentment and whatever other yuck emotions that come your way. I'm not saying react to them just feel them and let them go. All these crap emotions have something to teach us.
Give yourself permission to detach as much as possible from your sister or any other family member you have a hard time with. You seem to already understand that everyone involved has been through a lot of hardship; this is a good start to forgiveness.
Hope you are having some good quiet time at home with the storm! Here in the Rocky Mountains we just have sunshine. Stay safe and warm!