You've gotten some excellent advice so far.
But I'd like to add - please also have some empathy, understanding and patience. Just because you ended up being the most deserving of captain doesn't mean Bree was totally undeserving of it. Yes she apparently made a nasty commet, but she did so in the heat of the moment. It was one unfortunate comment to one friend as an immediate reaction. If she had won, would you have really not vented anything, to anyone? Would you have not been disappointed, bummed, a bit scared about college?
Also as far as your reaction to all this - think about sportsmanship. As winner did you go over and shake her hand and congratulate her on being a worthy opponent? You are a leader now and you need to take the high road. Bree is disappointed but one comment doesn't mean she's planning a mutany, it means she's a normal teenager who got bummed out and let it show for a moment.