Teenagers and alcohol...

Okay so the reason I ask is because my step daughter is 13...we found out that during her camping trip with her mom n husband she had given her a can of mikes flavored lemonade...I honestly don't see y she would of made a decision to give her alcohol at such an early age(in my opinion)..she has been in trouble with two serious occasions with the police n even got expelled from her school, so I just couldn't understand her decision..thanks for the input ladies...