My daughter had a teammate like that, I had no idea until the dad said once, "oh, my DD almost beat your DD today. " It made all the girl drama from this girl I had seen come clear. They obviously taught their daughter that teammates are to be beat and to this day, even though they are at different gyms, this girls attitude and need to best/beat her former (and current) teammates is still there.
I teach my daughter to do her best and not worry about her placements compared to teammates. I teach her that when they all do well, they do well as a team. So I always talk positive about her teammates and encourage her to be a good teammate, even when I don't particularly like a parent. They are, after all, just kids.