I think you're more concerned she might cheat while drinking, not so much about the drinking.... Right?
If she loves you, I don't think she would cheat drunk or sober.
You have to focus on you & hopefully she will follow suit.
If not, you will have to make a decision if you can accept her drinking.
You can't make her. But you can lead by example.
It's a struggle when you're young. Best wishes.