OK DN. In the same way that I said you needed to tell your friend you also need to speak to your sister. People need to know that have decided to stop gambling. If your sister wants to go to the casino then that is her choice, you accompanying her though shouldn’t be an option.
You also seem to have fairly easy access to quite large sums of money – how can you change that?
Make sure you get banned from that casino, for life/the longest option that they give.
Keep posting.