family VS honesty

So I have come to the conclusion that one of the hardes things to balence in life is honesty and family. I mean we are always taught that we should be honest and on the other hand you always put family first so what do you do when you have to tell your cosin that she is a a stupid whore. I know I know thats a horriable thing to say but even though she is family how dose that make her any differnt form one of my friend or any random person. So my problem... should I tell her what I think or just keep my mouth when it comes to my pro and con list the shut your mouth side is longer and is filled with more reasons to make my life easier but the tell her side is filled with more its the right thing to do reasons. So I guess I will continue to compare list and see what happens