@MasterSimper This sounds more like a family problem than a woman problem.
With that in mind, the first question you must know the answer to is this: do you want your sister as a part of your life? Is a relationship with your sister worth it?
Yes, some may say "but she is family!" You don't choose who is related to you, but you do choose whether they are worth having a relationship with. And I do not think severing any ties should be done on a whim. It should be done with proper merits.