Your friend may face health risks, for example overdosing on drugs or mixing drugs and alcohol, she may harm herself if she gets behind the wheel, and she may harm others as well, for example if she gets into an accident. To safely and legally enjoy the celebration, she can choose to abstain from these substances and thus eliminate the risks. If not, she can at least have a designated driver who will pick her up at a specific time to safely bring her back home and cause no harm to others.