The risks of gambling are very dangerous that’s why, I empathize with this difficult situation the mother and her son are facing. It feels bad just to hear about someone losing money, what if when it is taken without permission from a close and loved one who worked hard to make it.
About the mother's reaction i find it normla for her to feel deeply upset and disappointed, regardless of whether her son had won or lost while gambling. The loss of trust and the breaking of boundaries are a serious issue that should be fixed and discussed well between a mother and her son.

If I was in the mom’s position, I would be focused on teaching and studying well the underlying problem of unauthorized gambling and the breaking of trust it represents. even with winning a big sum of money from that bet wouldn't change the fact that the behavior was irresponsible and disrespectful to me. It's important to approach the situation with understanding and seeking to educate her son about the consequences of his actions and helping him learning a lesson from this experience. Beside that it’s important to always be behind that son and monitoring him well.