My Sister's betrayal

So I asked my sister several times if I could help in any way with the wedding and always got the same response. "No, there's nothing that you can do". So she posts on FB how she couldn't have pulled off the wedding without my brother and his loving wife.

Now let me tell you about my brothers so called loving wife. She calls my brother every name in the book and then some. She doesn't clean house. She adopted my brothers daughter from his first marriage a year after they got married (she was 13 at the time) and then told her she should go out and "Fuck whoever you want". Now you tell me what kind of "Mother" tells a 13 year old to do that? She is still verbally abuse to my niece (who is 24, married and has a child of her own now). My niece can't stand her. This so called loving person uses her two sons against my niece if she doesn't do something she wants her to, she won't allow her to see her brothers. She treats my parents the same way. I was smart and cut off contact with them several years ago, except on the rare family gatherings (Easter, Thanksgiving, Christmas) and if I can get out of those I will this year. And this is the person my sister choose over me to help with my niece's wedding.

I copied what my sister wrote and sent it to R. We talked about it when I got home and he told me I couldn't tell her to F off. I really want to do it. I'm tired of her hurting me. And yes, I know I am the one allowing her to do it. So it stops now. I will no longer allow it. My sister you no longer have power over me. You will not hurt me again. I don't have to see you ever again. I don't have to allow you into my life. I don't have to give you the power to hurt me. I take it back. I banish you from my life. Don't come crying to me when you want something as you always do. Go away be gone.

I sure wish it were that easy but I'm sure going to try to remove her from my life. Wish me luck. Why can't we divorce our families or can we?