^
As OP says, this girl spoke directly to the employees of this casino and they did not respond to her request. So it seems to me that without the involvement of law enforcement agencies the case will not move forward.
Definitely, because the threat level of the girl to the casino owner is near to zero. With the authority, the operator will be alarmed and threatened because there is power backing the group that is giving warning to the owner. If the Operator has no backer then for sure, it will follow the warning of the authority and will not accept minors to gamble in his place.
In general, if I were this girl I would ask someone to film minors playing in the casino and try to spread this information over the Internet. I think this kind of video would quickly find support among people who are fighting with this kind of violations.
That's right, evidence is always the best weapon against illegal activities, just be careful to not be spotted or get known by the illegal gambling operator because we never know what these people can do when they are cornered and start losing profit.