You don't say how old the little boy is, but is it possible for him to learn to reflect dd's emotions? I'm thinking of the method I read last night in The Happiest Toddler on the Block book (thanks to the other post for recommending it - pretty good book). Depending on the age of the child, they could learn to talk to the other child in terms of telling them, "you're upset! No No NO, etc. " and showing some empathy. This might help dd feel listened to and decrease the screaming? Just an idea.