DD is a confident, assertive child who is generally smily and well liked. When younger she would be rather over-bearing if she wanted something (ie snatching, hitting - by younger I mean aged 2-3ish)
I have always tried to talk through with her how to manage difficult situations, and express displeasure in inappropriate behaviour (hitting etc).
I was a very shy, quiet child who was very eager to please, and struggle with the correct level of assertiveness - hence asking for opinions.
Tonight dd came home from school (her first week) to say when she was in the playground she was kicked in the back by some children who stole her toy and pretended it was theirs. She told the teachers and peace was restored (other girls were told off as I understand it). Later that day during another playtime she went indoors by herself to get something and the other 2 girls were in there. They (in dd's words) "started being mean, saying they didnt like me and didnt want to be my friend" DD was not at all upset whilst telling me this - she seems to have made a few friends of her own.
However she then told me that she handled this confrontation by telling the girls "This can't be a very nice school if people like you are in it saying horrible things - I will ask if I can move schools"
DD was very proud of how she handled the girls, who then apparently said "good" 
I have no other children and would never have dreamt of standing up to these two girls - and I admit to cringing a bit and thinking that dd is just as bad as the girls arguing with them about how nice they each are 
I am well aware that dd could easily grow up into a hideous child who exerts authority and may even bully other children, and so I want to teach her the correct way of dealing with similar situations (which inevitably will occur as she meets people who clash with her)
What would be an appropriate reaction to this (trivial I realise
) issue?