Total frustration

My sister sent a picture of a naked man to someone on facebook-you did not see full frontal but you did see buttocks and it was on face book for all of my sisters friends to see. I  am a friend and I saw and I told my sister that it was inapropriate for her to post that.  so she appoligised and then somone said that it was funny and not offensive.  I told her as Christians we have to be careful not to let the world into our lives and the world is watching us and we can't let them see us doing things that is wrong.  Besides would you send it to Jesus if not then you should not send it to anyone.   She said someone that goes to our church saw it and thought it was funny and that even the preachers wife sends stuff like that around.  Now what .  Every time I see these people I will be thinking about this.What now???? To me it is stepping over the line.