Sister needs my help with something she stole

I'm a 22 year old guy, and I have a sister that's 17. <br><br>Kinda in a weird situation and I'm not sure what to do. My sister has stolen an expensive necklace from a family friend when they came over to visit our place last weekend. It's a diamond necklace that costs a lot, and I can't believe that she did this.<br><br>I'm really angry with her, but I still love her and I want to help her. I don't want her to get caught, and I feel protective of her.<br><br>The necklace is in her room right now, and I'm worried that it will get caught before she has a chance to get it back to her friend. I don't know what to do, and I hope someone here can give me some advice.<br><br>I don't understand why she did this. I don't think she did it because she's broke, because my family is pretty rich. She had no reason to steal the necklace, and it just seems like a weird thing for her to do.<br><br>What can I do to help her?