Z.R.
I have a 28 month old and noticed her being really bossy with the dog. She'll say, "No," "Don't touch," "Get." She'll even sort of kick at him. I realized with some shock, that she gets it all from me. I'm talking to the dog the way dogs are commonly spoken to, in short, stern phrases I'm sure he'll understand. When he's getting into something, I'll use my foot to guide or herd him away--never kicking or even touching him with my foot--just to guide him. Well, our toddler doesn't see that, she just mimicks. She uses my exact words and tone, so I've actually had to change the way I interact with the dog so that she doesn't pick up on what I do and misinterpret it and then act that way to others, aside from the dog.
She must be hearing similar things being said and incorporating them into her language. But aside from the language used, there is her frustration in thinking that there is one way to do something it has to be her way. That's the hard part, which will take lots of patience and understanding to help her through.
When I've worked with kids and with my own, I find it helps to be sympathetic toward them and say something like, "You're upset because the kids wanted to play with different rules. Yeah, that can be frustrating." Offer a hug or a walk. When they calm down from the initial upset, that's a good time to talk and help them change their thinking about something.
You might say, "You know, other people have different rules sometimes. Ant that's okay."
Help her problem solve, like coming up with rules everyone agrees on or offering another activity if they can't agree.
It's tough and we parents do our best. Good luck!