My "Best Friend" steals from me?

My friend has recently started stealing from me. The first thing she attempted was my BRAND NEW tanning lotion that was $50. and then about two weeks later she steals my FAVORITE soffee shorts! zebra print! and the weirdest part about this situation is that she has WAY nicer stuff than me! Her grandma jackie buys her anything she wants because shes a spoiled bit** like that! Pardon the language, but GOD. Who does this?! How can i get her back and never make her wanna steal from me again?