I had a few thoughts while I was reading your post. The first one is that you really can't change or control anybody else. As difficult as it is to watch our kids wander down a path *we* know can be painful, beyond sharing what our experiences have been and what we have learned, I think the best we can do is be a support for them. We can listen but not judge, and not even advise ~ unless we've been specifically asked (even though we're *aching* to give advice!). (And, even when we've been asked specifically, advice is a dangerous thing to dole out!) Sometimes, just being there to listen deeply is enough to allow our kids to find the answers they already have in their own hearts, and *they* can best work out what to do. All they need from us is to love them for who they are and hold space for them.
But, two other thoughts also sprang to my mind. First, there is a danger of labeling your daughter "bossy." (I'm not saying that you're doing that, but it's something to watch for.) My suggestion, if you want to, is to pick up a copy of "How to Talk So Kids Will Listen and Listen So Kids Will Talk," by Faber and Mazlish (I'm sure you can find it at the library). The last chapter (I believe) talks about the pitfalls of labeling (even something like "she's always such a good girl"). It's a great chapter! I think it's the best in the book!
The other thought was to consider perhaps redefining (in your own mind) the characteristics you are now thinking of as "bossy." Consider taking a few minutes to explore the positive aspects of the behavior that has earned her a descriptor like "bossy." Ask yourself what's good about it: does she have a strong sense of order? She's probably really creative. She probably has a world view that means a great deal to her. She's probably passionate. The world needs passionate people with a strong sense of justice. If these are her natural attributes, that's a good thing! Try to find what's so wonderful about her "bossiness" and how it might serve her in the future.
As best as you can, try to reinforce to herself and to you the good things about her personality traits! Even if you think to yourself, "I love that she feels so strongly about _____." See how that makes you feel differently about that part of her. And, if you can convey that to her, imagine how bolstered she will feel!!
Some kids are more sensitive then others, especially when it comes to their sense of order and what is "right." It's not necessarily rational, but their need for having and enforcing the kind of order *they* think is right is paramount to everything else, even if it costs them a friend, sadly. It may be something that she'll just need to outgrow. And, it may be something she's willing to brainstorm with you about. (Brainstorming is also covered in "How to Talk...")
The answer to your question, "How do I stop my daughter's bossy behavior?" I believe, is you can't. The only person in the world you *can* control is yourself. And, your daughter will find out eventually that the only person *she* can control is herself. Some folks, many folks, never learn that and never accept it. But, the sooner we realize that, the better our relationships can become.
I hope that's helpful, S.! It's a great question, and I thank you for asking it!
P.S. Please feel free to contact me if I haven't been exactly clear (it's a long post). I'd be happy to clarify anything I wrote that's not exactly making sense.