I am not suggesting that the sister stay silent, I am suggesting that she deal with her sister in law, possible her brother. I was taught that when adults have a personal conflict, then the adults involved that deal with it, they don't drag the rest of the family into it, or try to make people hate the other person. Would it be acceptable for the bride to go to her family and tell them how horrible (she feels) the sister is being? No one in this situation is a child, their parents do not need to be involved.
It is not giving in to deal with private problems privately. She should go right up to her sister in law and tell her exactly what she thinks of the situation, and tell her brother as if needs be (he is directly involved in the situation). If she feels her sister in law is being a bigot then she should tell her so. Then the three of them (I'm including the brother) can try to work out their problems, or go their separate if all else fails.
The sister is not being abused, or bullied. In one instance, her sister in law was terribly mean to her.
Without background, pattern of behavior, or any other information what so ever, the bride had been dubbed a bully and the sum of all evils. It has been suggested that the sister attempt to ruin her brothers wedding by convincing everyone not to show up, send mass emails telling everyone what a horrible person the bride is, and attempt have her publicly shunned. Can people really say this is not retaliation?
I have seen on this board, that people can terrible hang ups over things that I find to be ridiculous. Everyone has them, (including me) especially to things that have never been part of their reality. These things take time to adjust to. Sometimes people say terrible mean heartless things, and until the person that was hurt points them out they don't realize just how bad it is. Maybe they will have a moment of clarity, maybe they will just go on being a horrible person, the only way to find out is for person they hurt to tell them just how appalling their behavior was.
If you were judged only by your worst moment would you come out smelling like a rose?
Dignity and grace are do not go away when someone else is crass or nasty, that is when they are needed the most.