To me it sounds like typical behaviour - my sister and I are 18 months aprts and we are very different in personality. She is a very strong personality, whereas I am more easy going, keep the peace. She is a clan & neat freak, I am a little messy. We fought alot during our teenage years. The fighting was mainly verbal but occassionally physically. The verbal 'I wish you weren't my sister' is for maximum hurt factor....Whilst some siblings can't stand each other, most just say hurtful/nasty words for maximum impact. I am not sure how old your DD's are though. Do they share a bedroom? We did and it was a nightmare! At one time my sister put a line in the middle of the room so I didn't go on her side! lol Perhaps try putting them in seperate rooms/our of each others way so they have minimal interaction with each other.