Not wanting to forgive her (yet) and avoiding her are 2 different things. But I understand this.

My answer for the other question you linked I think are still valuable but I'll try to add some more things.

What would she need to do to be forgiven

It might sound like a stupid question, but what would she need to do to be forgiven? Would she simply have to say sorry and it would be over? Knowing this and giving this practical option to your family and sister might make it easier for her to take the first step.

Bring across your message

It might just still be they don't fully realize where you are and how you are still feeling. Writing a letter will help you to process it and for them to emphasis it. Think of the following points

• The hurt from your sister is still real.
• Family is already broken apart (especially for religious people it is good to know that their life is not perfect, to break religion and get out the basis behind their faith).
• She has not asked for forgiveness yet and she will have to take the first step.
• You blame your parents for still blaming it on you.
• This also hurts you.

Not forgiving ≠ Avoiding

While it is understandable that she hurt you and you don't want to talk to her, avoiding her at all cost based on this, is only hurting you more. Not going to family occasions because she is there or other things (it might be a good excuse not to go to family boring occasions but that to the side).

Get over

Whatever it was she broke your relationship, or spilled a big secret. Try to leave it in the past as something that happened in the past. Don't let it influence you in the future. You have your whole life ahead of you. Don't let this be ruined, enjoy it as much you can :)

All I can say is that it's probably best for you to start forgiving her, as it will set you free. By forgiving her you are conquering yourself to no longer be influenced by your sister. But I can easily say that not being in your situation.

I want to wish you best of luck and and to add one more thing

Include an external party

Everybody always says get a therapist but in my life it was always friends who helped me out. The nice thing about friends is that they are on your side (so it's quite safe) but they can tell you when you are over doing something.