I think if you confront her, there is a possibility of things going bad. I think that a nice talk with mom might be better. If your sister said these things in front of everyone, your mom must have heard them too. Telling your mom that you might not be coming to family functions because of your sister, she might have a talk with her. If it were my family, that is what I would do. It sounds like she thinks that she can act anyway that she wants. If she were told that she wasn't invited because of her attitude, maybe she would rethink her actions and apologize.
