I am a Governance Manger for the Department I work with. Every day I have to make very hard decisions and some of them affect people and not in a pleasant way. But at the end of the day there are rules and the rules are there for everyone to follow - there should be no exceptions. There are time when we can make the rules 'work' for us which we some times have to do as unfortunately not every thing is black and white.
Yes it doesn't feel good when you have to make this choice - and it hurts sometimes and I have lost friendships over similar things but at the end of the day we know what is right and wrong - even kids - and people make decisions some good and some bad - but they make them not you. If she is that good she will pick herself up but essentially at the end of the day she cheated and would it have been any different if it was one of the students at the bottom end of the class???
It is a hard lesson in life but better to learn it now rather than later on down the track when the consequences can be more devistating.
You did the right thing - never comprimise your standards and morals cause once you do you will never get them back.
Karl