drug use

My sister is going out tonight and she lied to my parents about what she's doing. It was the third time she lied this week and they let her get away with it. She has a major drug problem It's getting to the point that she's taking half the Advil in a week for hangovers, and she'll eat a lot just to get the drugs out of her system. And she wastes all her money on drugs and makeup just to look hot. She admits she hates drinking but she'll still go out and do it. When my older sister used to do it in highschool my parents called the cops on her and didn't want her to go out anymore but with the younger one she'll just let her do it and say "well they're young and they just want to have a good time!" Which is obviously justifying what they're doing.