Well.. I hope that she learns from her mistake. These sort of issues arise when people who are new to gambling indulge in it, without learning about the rules and possible consequences. A lot of people start like this. Some of them are scarred with the initial experience and never venture again. Some others learn from their mistakes and become more responsible for their actions. And then there is the last category, who lose their mental balance and start chasing after the losses. And we all know which group will end up in big trouble.
Obviously, they know the risk behind gambling but greed will not let them be, they will make decisions that will hurt them and when it doesn't favour them, they manipulate people around them, greed people are insatiable with this habit. When they have money, they spend recklessly the way they want and when they notice that the money is going zero, they risk it to bet thinking the money can be double and if this don't happen, they cry victim. Almost everybody on earth knows what gambling is about and she knows exactly what she was going into, she is not a baby.
if he knows gambling hurts him why should he follow it. not many people are ruined by gambling. he knows the limits in gambling. He should be an adult at that age and can think about that. but if it's like this, wouldn't it be a good idea to take him to a psychology doctor? I'm sure that can help him.
The subject says it's a she and you are consoling her as a he.

Don't act like you don't know that they know what gambling is/was about, even if she don't know. She could have just try it with a few dollars and see the outcome and if it's not favorable thing to play, she could have stop but from OP explanations, she lost a bet and was looking for sympathy with cry, is that how life works. Next time, she will learn better, life itself is not fair.