not to highjack this thread, but spaghetti - I am having this exact problem with my DD9. She is constantly rude, and I am constantly saying "is there a way you could say that that would make me actually want to help you?" and then she says it more politely.
And sibling rivalry is horrible in my house, a great deal of the time because she takes potshots at her older brother.. example: if he says he loves something, she will immediately chime in that it is the worst thing in the world.
I will have to go back and read the beginning of this thread - I need to do something about her behavior. For a long time I thought it was due to anxiety, but now I'm wondering how to change it because she won't survive long in the world this way…people will knock her down hard.
