What is the best way to handle someone who seems to think it's acceptable to ride roughshod over others, and when they express hurt or offense they're told they "can't handle the truth"? The comments and remarks made are deliberately hurtful and inflammatory, and yet the relative involved makes out they are only being honest... 
The difficulty is, this relative is extremely clever and articulate and can turn any attempt to address the issue back on the person who is the victim of the remarks to make it appear that they are at fault... No one else seems to be prepared to stand up to her for fear of being a victim of their sharp tongue themselves, so they get away with it time and again. Although I've never been on the receiving end, I can't bear to witness it, but want to word myself in a way that it isn't turned around against me, if that makes sense?
TIA for any advice.