It is clear that the mother was surprised by what her son did without taking into account whether he lost the money or made gambling profits from it. This is the same as any parent would feel after discovering two surprises: The first is that the son practices gambling, and the second is that he has the audacity to steal in order to play. This may be one of the most dangerous symptoms for a child who still needs the care of his parents.
Personally, I will rush to provide psychological support to my son, including monitoring his activity on the Internet and following up on support from psychological specialists. This is the least that can be done as a first step, regardless of any amount spent by the child.

Regarding the example in your story, the mother could be considered extremely reckless if she insisted on tracking down the lost money without taking into account the behavioral stage her son has reached.