Hi dingdong, is the book helpful? I'm on the look out for something like this to give me new pointers....... My DTs are younger but all 3 of my children are currently testing me to my limits with shouting and barking at me/each other. My DD1 was never like this before and its sad when you feel you've done something horribly wrong.
How would your parents handle it? I think you must go to the wedding as otherwise she will learn she has control over these situations.
Before you work out how to go forward, do you feel 100% happy that there is only minor issues at nursery? Friends can be cruel and it comes and goes by the hour (my DD1 has similar issues in the school playgound but it changes day by day). If there is something 'bigger' going on at nursery (and I mean along the lines of one child that has taken a dislike to her) then I reckon you need to take her seriously and ask her what she'd like you to do. A quiet word with nursery maybe? A session you sit in on? Let her feel supported? Make a friend of the PITA kid which in turn gently pressurizes that kid to lay off?
Otherwise, if you are happy her nursery complaint is just the vehicle for her outburst then I would be inclined to issue some kind of punishment. Try never to do it when you are angry or shouting.
A big punishment for my DD1 (and I only do it if things are really awful) is to go to bed before the DTs. Could she go to bed before her sister while her sis gets an extra story? I make sure I tell her its going to happen earlier in the evening (I take her to one side and tell her quietly and clearly, this way it doesn't come as a hideous surprise just before bed provoking tears and not whilst I'm in the throes of anger and shouting "AND YOU'RE GOING TO BED FIRST TONIGHT YOUNG LAYDEE" )
My DP told me a supernanny technique (I haven't seen it so I don't know) is to put one piece of pasta in a jar everytime there is behaviour you don't like, then a punishment once you have 5 or 10 or however many.......Personally, I always go straight to the punishment as I don't do clutter For faily dodgy behaviour, I give two warnings and the third time its early bed or up to rooms with the door shut to play alone, away from the family.
I hope I don't sound like I know everything. Its just ideas.....its not working that well in my house but I hold onto hope that if I keep going with the same rules and the same outcome I will win through.