This has to feel overwhelming to you. She needs to be held responsible for her actions, but also needs professional help imo. You can't make anyone stop anything, they have to do so themself! Don't take on the guilt that this disorder/illness tends to put on family and friends. And don't take on the financial burden either! If you do that, then everyone in the family will go down with the ship!

Take care. You can also get help from the Gamblers Anonymous organization.