This investment return makes it more or less certain that this is a scam. A 50% return in a month, on just cash, is absurd. If they were generating those returns, why wouldn't they keep more of that 50% for themselves? The only answer is because need to promise a lot of free money in order to attract victims.
First, have her ask her family for the documents and materials explaining the transaction - receipts, contracts, prospectus, pamphlets, whatever. I am guessing that documentation is minimal, maybe no more than a claim ticket. Criminals usually do not like lots of documentation of their crimes. Legitimate ventures usually do not mind explaining the details to their investors.
Then, have her ask her family how much money from this casino venture they have withdrawn and taken home, versus how much they have reinvested. Odds are they reinvest every bit of it. All the criminals need to do is flash some cash and trust that most or all of it will be "reinvested." They just need enough circulating currency to make it look real. At the end, when they have drawn in as many suckers as they can stand, they leave town.
Finally, have her warn her family it is a scam and tell them it's their fault if they lose everything. They are probably too far gone, but maybe this will slow them down. if nothing else, it will set the tone for when they come begging for money.
If you're feeling public-spirited, you might try turning over some information to local law enforcement. But I think it's wisest to avoid the criminals entirely.