How do you react?
The most important thing is to keep calm and not endanger your relationship by overreacting. It's possible you misjudged the levels. Find a quiet time to talk but don't accuse your daughter - just ask her a direct question. Remember to explain that your concern comes from wanting to keep her safe, and that you won't be angry if she tells you the truth, even if this is that she has taken the drink.
If your daughter admits to it, you'll want to find out why she's drinking alcohol secretly like this. But try not to jump to conclusions because it doesn't mean she'll become an alcoholic. Instead, think about why she might be behaving like this - does she want to see what alcohol is like, or is she testing the boundaries or getting back at you for something? You could discuss with her why it's not acceptable and ask questions to make sure she understands. Be firm but gentle, and make it clear what the consequences will be if it happens again.
