I know this isn't the answer you want to hear, and I know that you're angry, and I didn't read the backstory to this, but I've realized pretty recently that forgiveness feels good. To be able to let go completely and just feel sad and feel sad for the person who wronged you is a beautiful release. I've learned it's important to feel, and to feel lightly, but it's also important to be able to let go. Your sister's reaction to honest forgiveness might surprise you, and it might even bring you closer.

Just my two cents.

I'm not telling you what to do. It's been some years since I was 19, but I remember feeling very intensely about a lot of things.