J.K.
I love that you recognize this as a leadership quality and see the benefit of trying not to squash it. I think that this is a pretty normal thing at this age and for a first born girl. My daughter used to want me to color with her and then try to tell me what colors I could use and what color I had to color what things in the picture. I told her I didn't want to color with her when she did that, and the reasons.
I do think it's important to teach her that there are different ways to do things, and that a way that is different than her way is not necessarily the wrong way. I have a little boy in my daycare right now whose mother has passed down the "one way to do things is the only way..." and he has social problems, and an inability to cope with changes and things that aren't done his way.
With the awareness you have and what you've said here, I don't think that your daughter will have a problem with this. It will be a phase of behavior and she might get some playmates who don't want to play with her when she has to make all of the rules. (The she'll just boss her brother until he's old enough to object :) I'd encourage her to be a leader by helping others who may not know how to do things and exercising flexibility with her. You could even make a game of it... I know that you like to put away toys this way... what's another way that we could do it? What's a fast way to do it? What's a silly way to do it... etc
Good luck!