Sister doesnt want to go to brothers wedding...

I found out recently that my sister doesnt want to go to our brother's wedding. She basically says that she has better things to do. "Its not like its a funeral or anything".... I'm kind of offended by it. I want to say something tobher about it but the only reason why I know she said that is because she told a friend, and that friend told me. I don't want to bring my friend into the middle of it... but its our brothers wedding! Our only brother!!