As I'm sure you know, I'm not going to treat you like a child about this. I do not think this is a Violet problem. I think this is you problem. I know it is incredibly difficult to look forward to something, like being named prefect, for it to slip through your fingers and go to someone else, but she is not wrong; she did not steal anything from you. A jury of adults decided she was the best fit for the position and if it has ruined your friendship, then perhaps it was the right call. As of right now, your response says your immaturity would not have suited the role. I have never taken you for someone who would sour a friendship over something that, I hate to say it, will not actually matter in three year's time. I know it feels important now, but it won't in by the time you graduate.
Now that it feels like I have been incredibly harsh, I will follow up with, you have a big heart, Anne, which is why this bothers you so much. Being friends with someone who lives an entirely different lifestyle is difficult, but not impossible. You have to work at it. Friendship is a verb, not a constant state. I know from experience what you can lose when you forget that.
You'll figure it out, I promise. I've attached some sweets to get you through the thinking process.