^
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.
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.
So we are talking about the physical casino here where they allow minors to gamble
I thought the physical casino was safe as they won't allow underage to gamble, but since they are allowing them, legal action can be taken against them. In online gambling, we can enforce the KYC which can be abused sometimes if parents allow their children to gamble on their behalf as the gambling houses never know who is playing online at the back of the computer but here the situation is different.I wonder in which country this is happening And whether the laws in that country are clear about prohibiting of gambling by a minor.