I am in tears. DD has been difficult all day, since I said she couldn*t go to a concert next friday. she has been fighting with her sister all fucking day long - teasing, winding her up, threw glass of water at her (not sure if true, as I wasnt in the room at the time). She has just spent 20 mins shouting at me, stood in my way, I had to push past her to get out of the room, physically threatened me, called me all sorts of names. I kept calm at first but then I have lost my cool with her, and shouted too. She is now in her room. I really dont like her 
I don´t know what to do...