I will advise you to tell your sister to stay clear from that website. There is really nothing that shows that they are legit. If she's not sure about it being legit, then it would be better to stay clear from it than play around with her money and end up losing it. That's still her choice to make.

If she was referred to it by someone she knows, then it's best to confront the person face-to-face and ask them for proof, but if it was recommended by a stranger, then it's better to forget about it. My own advice would be to forget about this. There are other things she can do than taking some dumb risks.