Your Mom is right. Everything she said happens in real life, in the flesh & blood, I have no doubt it happens online too. The reason being that it also, is real life.
The problem here is the argument being in the flesh & blood, it should be easier to distinguish the real from the fantasy. The problem is that it is not. That means by implication either she's right, and it applies everywhere. Alternatively she admits she's mistaken. Either way, on line, or off line. It has no difference. If she needs such an example of off line fantasy, bring up the subject of religion.
Here are some good hilights of the argument. Philosophy is the study of where the ideas bring us to. Theology is the bending of ideas to bring us to a desired destination. Science is the study of evidence. Each has their own failings. Philosophy can lead you to meaningful conclusions, but have nothing to do with the real world. Pretty ideas, but no application. Religion is simply "the will to power" in another form. * Science with no evidence, and no grasp on a situation falls flat. All have their elements of real world fantasy.
* BTW this (theocracy - belief you're guilty, but no proof) is where the law in the states is heading.