What are some definitive arguments against multi-level marketing (MLM) business structures?

My sister joined an MLM scheme about 3 years ago, and it seems to have sucked her in. The mantra of MLM companies teaches its members to dissociate with people who disagree, because this is negative energy. Usually I say to each their own, but in this case my close relationship with my sister has been severely compromised. The worst part is that she has sacrificed friends and family in the hopes of getting rich quick. Is there any way I can connect with her again, and even better, any way I could definitively show her that she’s spending her own money to sell products for another company who will never fully reimburse her.