Tell her to lead through example and positive encouragement, not criticism. Hustle on every play and be respectful to coaches, even when they're not looking. Help everyone understand what needs to be done, but don't order people around. Pick team mates up when they're not doing well, and let the coaches do the coaching.
I agree with this thought as well. Although DD is currently out with an injury, her college coach has asked her to attend practices and help out with things. She has somewhat of a leadership role, even though she will not be playing this year. All throughout high school she had no choice but to work on her leadership skills. She pitched for a team on which she was the only travel ball player. The rest of the team looked towards her for that leadership. Looking back on things, one of my focuses all throughout her development had been finding ways to help her hone her leadership skills. And, while I would like to think I had something to do with it, to be honest I think most of it came from some of her role models. As one of the better players on a younger team in an organization, she often had opportunities to play up with an older team. Two players in particular had very good leadership skills and took a liking to DD. She spent a lot of time with them and I see some of their personality in her. I believe their mentoring had more to do with her current leadership aptitude than anything I did. If you have any opportunities to have your daughter in a similar situation, I think it would definitely help. But its a matter of being around the right people; an older friend, a cousin, an older player... It doesn't even need to be softball related. Just spending time with a quality mentor can really provide a positive environment.
I'm not sure most teenagers/high school students realize the type of impact they can have on younger kids. When DD was 9 years old her and I were at the local field practicing. The high school pitcher at that time came over and started giving her pointers (completely unsolicited). Anything I could possibly say was completely worthless compared to what this high school pitcher did in 15 minutes. I'm not sure DD blinked the entire time...