You are your own person, responsible only to yourself. If your sister has done things to you that you don't want to forget, and that you don't want to forgive her for, that is your decision and nobody else's. Usually it is the case that having someone on your mind all the time that you are angry with isn't good for you; either forgiving or removing her from your life and mind as thoroughly as you can are the reasonable solutions. From what you are posting, the second seems much more reasonable. Especially if it is so bad that contact causes physical symptoms for you.

What your parents want is different. Understandable, but it's your life and not your parents'. If they can't accept you as you are - including not ever wanting to forgive your sister - that should be their problem. I'd suggest that whenever they talk to you and try to convince you to forgive your sister, you tell them as explicitly as possible that this is not going to happen, ever. Don't give them the slightest indication that you might ever change your mind. A sequence of replies would be: "No.". "Never". "Never in a million years". "Not over my dead body". And if that isn't enough you'd have to criticise your parents themselves. "Can't you understand what 'No' means?" "Don't try talking to me about her, ever again".

I heard someone say "Never burn bridges. Either leave them, or blow them up to smithereens. Nothing in-between". I also heard someone say "friends are the relatives that you choose". Make your choice, and do what you can to make your parents accept that choice. According to your comments, your sister isn't interested anyway.

You are your own person, responsible only to yourself. If your sister has done things to you that you don't want to forget, and that you don't want to forgive her for, that is your decision and nobody else's. Usually it is the case that having someone on your mind all the time that you are angry with isn't good for you; either forgiving or removing her from your life and mind as thoroughly as you can are the reasonable solutions. From what you are posting, the second seems much more reasonable. Especially if it is so bad that contact causes physical symptoms for you.

What your parents want is different. Understandable, but it's your life and not your parents'. If they can't accept you as you are - including not ever wanting to forgive your sister - that should be their problem. I'd suggest that whenever they talk to you and try to convince you to forgive your sister, you tell them as explicitly as possible that this is not going to happen, ever. Don't give them the slightest indication that you might ever change your mind. A sequence of replies would be: "No.". "Never". "Never in a million years". "Not over my dead body". And if that isn't enough you'd have to criticise your parents' actions. "Can't you understand what 'No' means?" "Don't try talking to me about her, ever again". Since you don't want arguments with your parents, combine it with a strong indication that this is only about your sister, not your parents. "I love you, but please try not to talk to me about her, ever again".

Why should you never give them any indication that you might forgive? Because any such indication only tells them that they need to work harder to change your mind, exactly the opposite of what you want. Give them a strong no ever single time and there's a good chance they will give up which is what you want.

So: Clear indication that you will never forgive her and you will never want to talk about it. At the same time clear indication that this is against your sister alone, and not against other people.

I heard someone say "Never burn bridges. Either leave them, or blow them up to smithereens. Nothing in-between". I also heard someone say "friends are the relatives that you choose". Make your choice, and do what you can to make your parents accept that choice. According to your comments, your sister isn't interested anyway.