Hmm... in this kind of case you might want to dangle the threat of legal action over your sister. The amount of money the stolen property is worth is enough to classify it as a felony. Even if your sister didn't steal it all, she can most likely be charged as an accomplice and could receive jail-time (or juvenile hall if a minor). Trust me, the threat of legal action dangling over one's head usually makes them comply with the injured party's requests.