At this point, all you can do is learn from it. I don't think you can say anything now without making it clear that you've been stewing about it and thinking poorly about her.
Your original post said you felt badly for the 2 people behind you, so some responders thought there were only two. Had that been the case, you should have given those people the front slot and assembled your group behind them. But since there were 50-75 (per your ETA), you were part of short-changing all of them. So, your friend was pushy and rude, and her friends were worse, but you were a part of it. If you con't stand up to an injustice, no matter how large or small, you're a part of the problem.
The thing to do is to rehearse a couple of phrases for the next time ("I'm sorry, it just wouldn't be fair to all those who came out early" or "Ha ha, Emily, I know you don't expect me to let you jump the line!") and find the backbone you admit you didn't have. You are "close friends" with her but too intimidated to be honest. So instead of focusing on your rude friend (which I agree she is), re-focus on yourself and why you allowed yourself to be rude to others you don't know in favor of someone you do know. If she's a good friend, she'll respect you. If she isn't and she doesn't, well, you've learned something about her too, haven't you?