How do I get my older sister to stop stealing my stuff?

Keep the things that are most important to you in your purse and keep your purse with you at all times. Keep other things that you don't want to carry around, or that would be impractical to keep around, in a locked makeup or accessory case (like a train case) and keep the key in your purse. You could also get a hope chest and put important things in there and keep that locked. If your sister sees fit to try to pick the locks on or pry open locked cases or chests, she should be the one getting into trouble at that point! If locking your things up will cause more problems than it will solve, put your most treasured things in a case or a box and keep them with a trusted friend (one of the many things best friends are for!) and just remove the temptation altogether. Good luck!