Why have you not gone to therapy to deal with this?
To hold onto so much anger, is not healthy. You AND your sister should have also attended together so you could explain exactly why she hurt you so terribly.. The Therapist would have backed you up on it too.
My stepmom's daughter was killed in a horrible accident (6 years). There have always been whispers that possibly the kids had been partially at fault, but my stepmom, knows in her heart in the truth and does not listen to all of this. She is still in therapy to help her through all of this. She like you will never be the same, but she has found a sort of peace.
I like t say "she is full of grace". She does not have time for anger. She does not want the legacy of her daughter to be any blame or anger. She knows it is a wasted emotion compared to the love and strength she can gain from others.
Your daughter I am sure understands your feelings, but she also knows family is a lifetime. She does not want any regrets in the future when you and your sister find peace.
Grandchildren will be next, and I am sure you and your sister will want each other in your lives to share the joys of your grandchildren.
Please please, find peace in your heart. I would hope what your sister said to you was not meant to hurt you, bu t rather an extremely poor choice of words.
Go to this wedding and make it the best memory your daughter and her fiance will ever have.
I am sending you strength.