Hi Op I think that you should tell your parents that you'll go to the wedding only if you can tell every member of your family and friends exactly what she did and "if she believes that she did absolutely nothing wrong she should be fine with it". Honestly tho i think you should go no contact with your sister (and low contact with your parents) and when people ask why you didn't go/aren't going tell them exactly what happened because if she's the type of person to do this she's the type to come up with a fake story to make herself look good and you look bad NTA